Probabilistic shaping (PS) is a powerful tool that can realize a flexible data rate and high spectrum efficiency. However, the performance of PS is closely related to the quadrature amplitude modulation (QAM) order, source entropy (SE), normalized generalized mutual information (NGMI), and achievable information rate (AIR). In this paper, we investigated the relationship between PS QAM order, SE, NGMI, and AIR performance for the first time in the visible light communication (VLC) system. Under a specific signal-to-noise ratio (SNR), the PS QAM order and SE in this paper can realize a high AIR at a preset NGMI threshold with the lowest computation complexity, which is just 0.1 bit smaller than the highest AIR. Simulation and experimental results show that the NGMI fluctuates between only ±0.005 of the preset NGMI threshold, which proves that the scheme proposed in this paper is feasible.