A built-in roller shade actuation device for actuating a winding drum with opposite ends rotatably mounted to corresponding frames and an outer side mounted with an end of a shade body includes an actuator assembled in the winding drum for providing a rotation power, a shaft mounted to one of the frames outside an end of the winding drum and inserted into the winding drum, and a gear pair mounted between the actuator and the shaft for realizing power transmission. A shell of the actuator and the winding drum are relatively fixed in a circumferential direction. The gear pair includes a planetary gear mounted to an output shaft of the actuator, and a fixed gear mounted to the shaft and coaxial with the winding drum. The planetary gear revolves around the fixed gear while being driven to rotate by the output shaft of the actuator.