Abstract: A reciprocating low-speed heavy-load hydraulic pump with a variable action area comprises a plurality of hydraulic cylinder units (3) and moving members (1, 2). Two ends of the hydraulic cylinder units (3) are separately connected with the moving members (1, 2) via mechanical structures. The moving members (1, 2) move relative to each other. The hydraulic cylinder unit (3) consists of a hydraulic cylinder (4), a reversing valve (5) and a one-way valve (6). The hydraulic cylinder (4), the reversing valve (5) and the one-way valve (6) are connected with each other via hydraulic pipelines. Based on different magnitudes of driving force, the hydraulic pump can proactively configure and form different combinations of hydraulic cylinder units, and further adjust the size of an equivalent action area.