The invention discloses a precision plunger pump for treating traces of fluid. The precision plunger pump is composed of an extending-shaft-type linear stepping motor, a piston, a pump body, a sealingassembly and a position sensing assembly. The extending-shaft-type linear stepping motor drives the piston to slide in the pump body relative to the sealing assembly so as to achieve linear reciprocating motion required by the plunger pump. The piston is connected with an extending shaft of the extending-shaft-type linear stepping motor or directly connected with a screw nut of the extending-shaft-type linear stepping motor; the motor extending shaft is provided with a hollow part or a blind hole, or the piston is provided with a blind hole; and when the piston moves towards the interior of the linear stepping motor under driving of the extending-shaft-type linear stepping motor, a lead screw can penetrate through a nut to enter a hollow or blind hole area of the motor extending shaft orthe piston, thus the axial length of the linear stepping motor is saved, and the length of the precision plunger pump is decreased. The precision plunger pump can adopt the different sealing assemblystructures and position sensing assemblies. The precision plunger pump is simple in structure, low in cost and compact in size.