The thermo-gravimetric behaviors under different atmosphere and glass transmission temperature（Tg） of self-made hyperbranched polyurethane（HPU） and UV-curable hyperbranched polyurethane acrylate（HPUA） were analysised with thermogravimetric analyzer(TG) and differential scanning calorimeter(DSC).On this basis，the thermal decomposition mechanisms of HPU and HPUA were investigated with the combination of themogravimetric analyzer and Fourier transform infrared spectrometer（TG-FTIR）.The TG results demonstrated that HPU and HPUA had a simtlar thermal degration behavior，both presenting three thermal degration plateforms.Comparing the decomposition behaviors of two compounds under air and nitrogen，their decomposition behaviors were found to be similar，but the former was more quick.DSC analysis indicated that when adding HEA，the Tg of HPUA was obviously lower than that of HPU.TG-IR analysis demonstrated that，compared to that under nitrogen atmosphere，HPU and HPUA decomposed more rapidly and thoroughly under air.The thermal decomposition mechanism of HPU was degradations of alcohol，urethane bond and ureido bond，respectively，and the thermal decomposition mechanism of HPUA was decomposition of hydroxyethyl acrylate，urethane bonds and ureido bond，respectively.