Abstract: The paper analyzed working principle of traditional mine-used blending devices of emulsion concentration and theirs problems of blending precision and costs, and introduced design of a reciprocate type blending device with single-piston which does not need explosion-proof design. The device makes emulsion concentration blending according to fixed area ratio which can make emulsion concentration be not influenced by change of water pressure and other external parameters, and it has high blending precision. The device does not need extra hydraulic pump and motor with low production costs, and it belongs to pure hydraulic device, so it does not need explosion-proof design. The test result showed that the device runs stably and each index reaches design requirements.