The utility model discloses a piston-type clayey soil pore water mechanical squeezing instrument which comprises a support seat, a press filtering device, a water sample collection bottle and a pressure applying device, wherein the press filtering device at least comprises a hollow column used for containing a soil sample; the upper part and the lower part of the hollow column are respectively connected with a piston and a base; the base is provided with a water guide hole and a water guide groove; the water guide hole is communicated with the water sample collection bottle by a water guide pipe; a filter screen and a filter membrane are arranged between the base and the soil sample; the pressure applying device at least comprises a lever mechanism and a double-rod bracket; a cross beam of the double-rod bracket is connected with the piston by screws; and one end of a lever in the lever mechanism is connected with the support seat by a bearing A and connected with two rods of the double-rod bracket by a bearing B, and the other end of the lever is provided with a balance weight device. The piston-type clayey soil pore water mechanical squeezing instrument is simple in operation and low in cost, realizes continuous pressure application and does not cause pollution for the water sample.