Aiming at a visible light communication system under the on-off keying (OOK) modulation with a rate of 100 Mbit/s and a bias current of 0.15 A, the influences of modulation degree on the performance of the communication system and the lighting effect are investigated by software simulation combined with experimental verification. The results show that the bit error rate decreases as modulation degree increases. Further, the smaller the distance is, the more sensitive the bit error rate becomes to the change in modulation degree. As for a 100 Mbit/s visible light communication system containing a 1 W phosphor-coated light-emitting diode at a set distance of 12.0 m, the modulation degree should be at least 0.1 to satisfy the threshold requirement of forward error correction. Furthermore, if the communication system requires a high reliability, the modulation degree should be between 0.1 and the modulation degree corresponding to an error rate of 0, and it should have no effect on illumination effect.