Sulfuric acid leaching is one of technologies that is developing for the treatment of scheelite. Here, the effect of H2O2 on mechanism of low-grade scheelite decomposition in sulfuric acid was systematically investigated, with emphasis on the phase transformation and kinetics. The addition of H2O2 effectively prevented the formation of insoluble H2WO4 film, thereby arousing the efficient leaching of W from scheelite and separation of Ca and W. The recovery efficiency was dramatically increased to 96.1% compared with that in the absence of H2O2 (71.2%). Remarkably, proper rising temperature was favor to improve the leaching of tungsten, otherwise unfavorable effect would occur at higher temperature due to the decomposition of H2O2 and generated tungsten peroxide as well as the formation of H2WO4. Furthermore, the concentration of H2O2 affected not only the leaching efficiency but also the crystal structure of calcium sulfate. According to the kinetics investigation, the process exhibited a lower apparent activation energy of 49.71 kJ/mol, suggesting that the leaching process was affected by a chemical reaction. Eventually, the thermal stability of tungsten peroxide was evaluated and the pure orthorhombic phase WO3·H2O with a flower shape was achieved by heating the lixivium. In the whole process, the coordinating ability of H2O2 with tungsten was used for leaching scheelite and the poor thermal stability of tungsten peroxide was used for extraction of tungsten from solution.