Abstract: To design effectively PMMA tube structures in temperature decreasing equipment for gas generators,one dimensional transient heat transfer mathematical model of PMMA thermal degradation is established in the radial direction of a cylinder coordinate system.The formula between the average temperature of PMMA tube thermal degradation and average rate of temperature increase on the interior wall surface is deduced.The zero dimensional mathematical model of fluid flowing through PMMA tube is established.The thermal degradation process in interior wall through which generator gas fluid flowed in the radial direction is simulated numerically under the condition of experimenting with the above models,the degree of gas temperature decrease for PMMA tube interior wall thermal degradation is simulated.Thus full support is provided for engineering design.