Based on analyses of the basic theories and rules of sustainable development, the characters of agricultural mechanization, as well as the opportunities and challenges for China agriculture, the relation of agricultural mechanization and agricultural sustainable development is studied.Development and harmony are the two cores of sustainable development. Development is to promote the ability of utilizing natural resources by substituting advanced productivity for underdeveloped one, and harmony is to regulate the relation of nature and human, along with that of human and human. Agricultural mechanization is the trend of productivity’s development, and human’s being in harmony with nature is possible and necessary in the course of agricultural mechanization development. Its advanced function should be sufficiently brought into play and its disadvantage function should be avoided by all means, all of above have been proved in agricultural production in many countries.As a traditional research focus of valuing the ability of agricultural sustainable development, many systems of valuing indices are not used in practice widely because they either contain too many indices or are difficult to measure. Now the researches are going on. In the new valuing indices which are divided into restricted factors and harmony factors, a set of a scientific and practical valuing system which can evaluate the state and direction of agricultural sustainable development is proposed in this paper according to the idea that attaches equal importance to capacity’s building and harmonious developing. The state of sustainable development is valued according to departure from normal state. At present, China agriculture has stronger developing ability but poor harmony so that problems such as agricultural overpopulation, soil erosion and in excess of exploitation of groundwater have to be solved in course of development.Statistical data indicates that GNP per person and birthrate is closely related to the ratio of agricultural worker in all employees, which is closely related to the level of agricultural mechanization. In the course of urbanization and industrialization, human can promote national income and control the increase of population by improving industrial and agricultural productivity continually. It helps to deal with the sustainable development of agriculture and national income in the course of development. Those are very important to the countries that need farther development and have to control increase of population.The economic carrying capacity of plow lands is a very important concept with the economy globlizations. It can determine the minimum scale of maintaining agricultural sustainable development microcosmically, and help to estimate the optimal population in field of agriculture macrocosmically. According to the China economic standard at present, it needs about 2.0 hm2 plow lands at least for a peasant to maintain the ability of unsustainable development and the population capacity of China plow lands is about 250 million people. The population of 440 million in all of farming, fishery, forestry, and stock-raising is suitable.To carry out agriculture sustainable development, it is necessary to pay attention to building the capacity of agriculture sustainable development and to speeding up agricultural mechanization. Agricultural mechanical technology with high efficiency should be made use of firstly. Excessive and inappropriate use of agricultural mechanization can lead to resource waste and environmental destruction to some extent.In order to form an appropriate environment for agricultural mechanization development and improve the agricultural mechanization level, on One hand, marketization and socialization of agricultural mechanization service should be speed up according to the demand of productivity, on the other hand, related laws and statutes should be consummated.