Finite element numerical simulation based on transient thermalstress coupled analyses was conducted to understand the temperature, stress and dimensions for PBX cylinder during temperature rising. Results show that with temperature rising, heat transfers from surface to inner; stress augments rapidly at beginning, even arrives to 2.37 MPa, then reduces with temperature difference decreasing, the size of PBX cylinder is grown and its density is decreased by about 0.008 g·cm^-3. Numerical simulation can preliminary determine the regularity of stress distribution. And heating process has been optimized to try to decrease the rate of temperature rising and ensure at least 1800 s temperatureconstant time.