Provided is a method for preparing an epoxide by halohydrination, the method comprising: (1) halohydrination: adding H2O, a halogen(s) and an olefin compound to a reaction device for reaction to obtain a halohydrin; (2) saponification: saponificating the halohydrin with an alkali metal hydroxide to obtain an epoxide and an alkali metal halide; (3) performing a bipolar membrane electrodialysis of the alkali metal halide to obtain an alkali metal hydroxide and a halogen hydride. Also provided is a method for preparing an epoxide by halohydrination, the method comprising: (1) halohydrination: halohydrinating a halogen hydride, an H2O2 and an olefin compound to obtain a halohydrin; optionally, (2) saponification: saponificating the halohydrin with an alkali metal hydroxide to obtain an epoxide and an alkali metal halide; optionally, (3) performing a bipolar membrane electrodialysis of the alkali metal halide to obtain an alkali metal hydroxide and a halogen hydride. The method according to the present invention can prepare a halohydrin or an epoxide at very high selectivity and yield, and greatly reduce the amount of waste water and waste slag discharges.