Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak (J-TEXT) was presented in this paper.The principle of the plasma electron density measuring by hydrogen cyanide (HCN) laser interferometer was introduced. Room temperature triglycine sulface(TGS) detector was used to obtain the beat signal of HCN,and phase difference was measured by highspeed acquisition card DAQ2010. Based on the signal characteristics,a specific HCN processing algorithm was designed to eliminate the baseline offset accurately and process overturns of HCN signals effectively.As a result,plasma electron density with high accuracy and low noise has been obtained during the J-TEXT tokamak experlment.