The invention provides a preparation method of phosgene. The method comprises the following steps: mixing organic phosphine compounds disclosed as Formula (I) and solid phosgene, and reacting to obtain the phosgene. The organic phosphine compounds with higher reaction activity are utilized to depolymerize the solid phosgene, so that the depolymerization speed of solid phosgene is high. Furthermore, the organic phosphine compounds and solid phosgene are mixed and then heated to further control the depolymerization speed of the solid phosgene, so that the depolymerization rate of solid phosgene is high, and the phosgene has high purity.