Abstract: A thermogravimetry analysis device and electric conductivity method were used to study the effects of five flame retardants (Al(OH)3, Mg(OH)2, DBDPO, C3H3N6 and zinc borate) on the release of HCl during pyrolysis of polyvinylchloride(PVC). The results show that both the maximal pyrolysis rates of Al(OH)3/PVC and Mg(OH)2/PVC systems increased about one time in the first stage, both the pyrolysis rate in the first stage and pyrolysis mass in the second stage of DBDPO/PVC system increased, the mass fraction of C3H3N6/PVC system in the second stage descended rapidly, the rate of maximal mass loss of zinc borate/PVC system also descended rapidly. Al(OH)3 could promote the system to release HCl and increase the amount of HCl. Mg(OH)2 could also advance the system to release HCl, but the amount of HCl decreased. DBDPO could accelerate the system to release HCl. C3H3N6 played a acceleration role of HCl emission in the initial stage, but an oppsite role in later stage. Zinc borate′s effect was just contrary to that of C3H3N6.