A camera module includes a circuit board having a supporting surface, a socket fixed on the supporting surface of the circuit board and defining a receiving space, an image sensor received in the receiving space, and a lens group optically coupled with the image sensor. The receiving space of the socket has an entrance and an internal surface. A block protrusion is formed on the internal surface. The block protrusion includes a first ramp extending from the internal surface to a center portion of the receiving space. The lens group includes a plurality of optical components. A slope parallel to the first ramp is formed on one of the optical components. At least part of the lens group is received in the receiving space and blocked by the block protrusion, with the first ramp resisting against the slope. A method for assembling the camera module is also provided.