Provided is a lens module assembly device for assembling a filter glass into a lens barrel of a lens module. The lens module assembly device includes a clipping element, a receiving element, and a pushing element. The clipping element includes a chamber configured for clipping the lens barrel. The receiving element extends from one end of the clipping element and includes a receiving portion for receiving a number of filter glasses. The receiving portion includes a resisting end received in the chamber and an entrance end away from the resisting end. The pushing element is inserted into the receiving portion through the entrance end until resisting against one of the filter glass. The pushing element pushes one of filter glasses out of the receiving portion into the lens barrel.