Abstract: In order to investigate the gain distribution characteristic of non-chain pulsed DF laser, based on the influence of collision widen and Doppler widen of spectrum on gain coefficient, the simple equations were given to calculate the gain coefficient using the variable output coupling method. Under the conditions of different output mirror transmission, utilizing the method of moving iris to scan sample, the DF laser output power of every sampling position had been measured on the cross-section of gain medium. For arbitrary sampling position, two independent gain coefficients were calculated which standard deviation was less than 3%. Average gain coefficient of DF laser was 2.594 3 m-1 and the non-output loss coefficient was 1.243 5 m-1. For gain coefficients of each sampling position, two-dimensional interpolation algorithm had been used to obtain gain distribution on the cross-section of gain medium. The calculation showed that the gain coefficients submitted to supper-Gauss-Poisson distribution which was high in the central and low in the margin. The investigation could provide a guide to design resonator and electrode structure of non-chain pulse DF laser, and provide a reference to analyze the uniformity of gas discharge of this laser.