A hydraulic power system for a downhole device, comprising: a first motor (10), a first hydraulic pump (11), a second hydraulic pump (12), a first main oil circuit A, a second main oil circuit B, a switching control module (13) and a first execution module (14). The first motor (10) has a first output shaft (101) and a second output shaft (102); the first output shaft (101) drives the first hydraulic pump (11), and an oil outlet of the first hydraulic pump (11) is connected to an input end of the first main oil circuit A; the second output shaft (102) drives the second hydraulic pump (12), and an oil outlet of the second hydraulic pump (12) is connected to an input end of the second main oil circuit B; the first execution module (14) is connected to an output end of the first main oil circuit A; the displacement of the first hydraulic pump (11) is smaller than that of the second hydraulic pump (12); and the switching control module (13) is connected between the first main oil circuit A and the second main oil circuit B, and is used to adjust the working pressure of the first main oil circuit A and the movement speed of the first execution module (14) by means of controlling the turning on and off of the first main oil circuit A and the second main oil circuit B. In addition, disclosed is a downhole device that comprises the foregoing hydraulic power system.