The invention relates to cast moulds, in particular to a detachable mould for manufacturing an oil pump plunger sand mould. The detachable mould comprises a bottom mould, wherein the bottom mould comprises a bottom plate, a mould core piece and a core taking piece; a blind hole, corresponding to the mould core piece in size, is formed in the bottom plate; the mould core piece is positioned in the blind hole and the mould core piece and the blind hole are arranged in a split manner; the core taking piece is connected with the outer side wall of the mould core piece. The detachable mould has the benefits that the production efficiency is improved, the production cost is reduced and economic benefits are increased.