The invention discloses a modular cart assist device, comprising a handle, a controller and a drive structure, wherein the handle is connected with the controller, the controller is connected with the drive mechanism, the handle is used for controlling the travelling direction and speed of a drive mechanism through the controller, and the drive mechanism is mounted at the bottom of a cart. The parts of the modular cart assist device are modularly designed, and the design and mounting of the assist device are simplified; the drive mechanism is mounted at the bottom of the cart, changing original castors is not required, the cart can be modified conveniently, and little influence is caused to steering flexibility of the cart.