To study the effect of buffer gas on the three-dimensional gas temperature distribution and output performance of flowing-gas circulation diode-pumped alkali vapor laser (DPAL), the beam propagation equation is introduced into the theoretical model of flowing-gas circulation DPAL in this paper. The effects of the composition and pressure of the buffer gas on the output performance of the end-pumped transverse flow cesium vapor laser are simulated and analyzed. The three-dimensional distribution of work temperature and output power are obtained. The results show that when using pure alkanes as buffer gas, the temperature in the vapor cell corresponding to ethane is lower than methane with same pressure, and the laser output power is higher. When the mixture of alkane gas and inert gas is used as a buffer gas, if the pressure of alkane is low, adding an appropriate amount of He or Ar can reduce the temperature in the vapor cell and increase the laser output power.