In the direct epoxidation of propylene to propylene oxide over TS-1, the effects of reaction pressure, reaction temperature, catalyst quality and concentration of hydrogen peroxide on conversion and effective utilization of hydrogen peroxide, and selectivity of propylene oxide were systematically investigated in acetonitrile solvent. The experimental results show that the selectivity of propylene oxide is not related to technological conditions at all, and is always 100%. Then the mechanism of propylene epoxidation in acetonitrile solvent, compared with that in methanol solvent, was preliminarily researched in order to provide theoretical guidance for selecting an advanced solvent in propylene epoxide technology.