Recently, a light-emitting diode (LED) was used as an optical source in the transmitter for underwater wireless optical communication (UWOC) because it has a large divergence angle that makes establishing the communication link easier. In practice, there are several discrete LEDs in the transmitter to enlarge its output power. However, with the increase in the number of LEDs, the parasitic resistance and inductance in the light source is larger too, which affects the quality of the modulated signal. Also, using more discrete LEDs enlarges the luminous surface, which is disadvantageous to improving the tolerance to water pressure for UWOC equipment. To reduce such influences, a transmitter is proposed with a chip-on-board LED array because it has a smaller luminous surface, parasitic resistance, and inductance. Using such a transmitter, a UWOC system is established and tested in a large experimental tank. The results show that it could realize a 19 m communication distance with a 30 Mbps rate in water with an attenuation coefficient that is about 0.26  m^−  1. The output power is 1.69 W, and the radiation intensity is approximately a Lambert distribution with a 120 deg divergence angle. Further analysis shows that the communication distance could increase to 90.5 m in clear water with a 0.02  m^−  1 attenuation coefficient, and the emission light could cover 86.5% of the solid angle of the hemisphere space. The speed is higher than the same class light source in the previous sea trails, and the combination performance of angle coverage area, distance, and speed is suitable for ocean engineering. The proposed method is useful, simple, low-cost, and pragmatic, which makes it easy to popularize and apply.