Modulation technology is the key factor affecting the performance of space optical communication system. Comparing the comprehensive performance of several typical intensity modulation schemes in a unified scale, five performance expressions of average symbol length, bandwidth requirement, bandwidth utilization, average transmit power and transmission capacity of 19 typical intensity modulation schemes are derived, and the numerical simulation is carried out. The comprehensive performance structure chart of each modulation mode is drawn, and the applicable scenarios of different modulation modes are given.