As an important evaluating method, the technology readiness level (TRL) can provide a better decision-making basis for the defense acquisition of weaponry, and can effectively reduce the technical risk of equipment development. The foreign evaluation methods of technology readiness level were briefly introduced, and the application of technology readiness level in the American ship-based laser system LaWS was studied. The LaWS system consists of five sub-systems such as transmitter-telescope, light source in military operation, diastimeter, target tracking sensor and control system. In the system development, in addition to a small number of custom components, a large number of industrial lasers, inertial measurement devices, sensors, video trackers and other commercial devices are adopted. A series of demonstration experiments were retrospected in LaWS system, the technical problems exposed in each test and the corresponding solutions adopted were analyzed, and the technology readiness level of each stage was evaluated. Finally, the research and development approach and the significance of battlefield deployment were reviewed.