A camera assembly, a method for tracking a target portion based on the camera assembly, and an electronic device are provided. The camera assembly includes: a first camera; a first motor for driving the first camera to move; a second camera, comprising a plurality of pixel blocks each being formed of a plurality of photosensitive pixels and configured to obtain a first photodiode pixel by capturing a target portion of an object to be photographed through a first part of the plurality of photosensitive pixels and obtain a second photodiode pixel by capturing the target portion through a second part of the plurality of photosensitive pixels when the target portion is detected; a controller, configured to obtain a global photodiode pixel, calculate a phase difference and control the first motor to drive the first camera to move to an in-focus position according to the phase difference.