Researches on the Porter hypothesis have paid more attention to the effect of the external constraint force of environmental regulation on green total factor productivity (GTFP), while ignoring the effect of internal force of market competition on GTFP. Using the panel data of Chinese manufacturing industries, this paper measures China’s GTFP with the global frontier MML index which is based on the EBM model. The paper then studies the effect of environmental regulation and market competition on GTFP. The combined effect of environmental regulation and market competition on enhancing GTFP is further investigated. The results are as follows: 1) The GTFP of the manufacturing industry has progressed during the study period and the progress of green technology plays a crucial role in promoting GTFP improvement. 2) The environmental regulation and market competition both have an obvious nonlinear effect of U-type on GTFP. Relying solely on the external constraint force of environmental regulation or the internal force of market competition does not promote the improvement of GTFP quickly. 3) As for the combined effect, improving market competition is beneficial to the positive effect of environmental regulation on GTFP. Market competition and environmental regulation show a significant combined positive effect, accelerating the arrival of environmental regulation inflection point. Thus the rapid improvement of GTFP requires the combined effect to be effectively exerted. However, only when the level of environmental regulation is strong or the level of market competition is high can a combined positive effect appear. The conclusion provides China with a meaningful reference for better implementing the policy of environmental regulation and market-oriented reforms to promote green economic transformation.