This paper presents a dynamic evaluation method to calculate the buckling strength of oilfield derricks. First, the linear relationship between the basic frequency and the ultimate strength of the cantilever structure with axial load is determined using the dynamic eigenvalue equations of the structure. Then, the basic frequency, ω 2 1i , corresponding to the load, N i, can be calculated or measured, and the linear relationship of ω 2 1i ～N i is plotted using the data mentioned above. The axial force corresponding to ω 2 1i =0 is the required buckling strength of the oilfield derrick. The suggested method can evaluate the buckling strength of oilfield derricks combining nondestructive testing with calculating. It is a convenient and practical method to estimate the carrying capacity of any steel structure. This paper presents a dynamic evaluation method to calculate the buckling strength of oilfield derricks. First, the linear relationship between the basic frequency and the ultimate strength of the cantilever structure with axial load is determined using the dynamic eigenvalue equations of the structure. Then, the basic frequency, ω 2 1i, corresponding to the load, N i, can be calculated or measured, and the linear relationship of ω 2 1i to N i is plotted using the data mentioned above. The axial force corresponding to ω 2 1i = 0 is the required buckling strength of the oilfield derrick. The suggested method can evaluate the buckling strength of oilfield derricks combining nondestructive testing with calculating. It is a convenient and practical method to estimate the carrying capacity of any steel structure.