In this paper, the symbolic structures of 19 typical intensity modulation schemes are introduced, and their slot error rate (SER) models in a Gaussian channel, weak-turbulence channel, and moderate-turbulence channel are derived and numerical simulations are performed. The results show that with the increase in the signal-to-noise ratio (SNR), the SER of each modulation mode initially decreases, but then, gradually plateaus. When SER stabilizes, the SNR requirement increases with the increase in turbulence intensity. The SER of pulse position modulation (PPM) is the smallest in all three channels. When the modulation order is small, the SER of differential amplitude PPM is the largest, and when the modulation order is large, the SER of on-off keying(OOK) is the largest, while SERs of the other methods are in-between, arranged hierarchically as the modulation order increases. These research results will serve as a reference for the design of practical laser communication systems.