The invention discloses a power control device for a hydraulic pump of an excavator. The power control device comprises an engine (5), a servo valve (7) and a pressure adjusting plunger (8), wherein the engine (5) is in driving connection with a first hydraulic pump (2), a second hydraulic pump (3) and a third hydraulic pump (4) with variable output volumes, and a guide pump (1) with a fixed output volume; a first stair surface (8a), a second stair surface (8b), a third stair surface (8c) and a fourth stair surface (8d) are arranged on the pressure adjusting plunger (8); an outlet of the guide pump (1) is connected with one oil port of a pressure adjusting valve (24); and the fourth stair surface (8d) of the pressure adjusting plunger (8) is connected with the other oil port of the pressure adjusting valve (24) through a tenth pipeline (27). The power control device for the hydraulic pump of the excavator provided by the invention is used for effectively utilizing the output power of the engine, preventing the location in a low power output region, increasing the working efficiency of a hydraulic excavator and increasing the use ratio of fuel oil.