Blue-green LED communication is considered to be an effective means to solve the problem of underwater short-distance high-speed wireless data transmission. However, as LED divergence angle is usually quite large, the geometric loss is great in such communication link, which would reduce the communication distance. Aiming at this problem, a method is proposed to compress the emitter angle of underwater LED array light source with the total internal reflection (TIR) lens in this work. First, the divergence angle of LED array source is compressed from 130°to 7°. Then, a communication transmitter prototype is developed with the source, and a test system is built in a large tank to test the performance of the transmitter. The experimental results show that the communication prototype designed in this paper can support a maximum transmission rate of 23 Mbit/s when the underwater transmission distance is 16.6 m. Compared with the case without TIR lens, the maximum transmission distance increases 9.3 m at the same rate. It shows that the method of secondary light distribution with TIR lens can effectively reduce the transmitter's divergence angle and the link loss of transmission system, enhance the transmission capacity of communication system. It provides a new technical means for improving the transmission performance of underwater LED communication.