The influences of main parts of an apparatus and channel to power of communication laser on spaceground optical communication slant link were analyzed. Based on the formula for signaltonoise ratio of receiving detector and bit error rate of communication, the simulation system of spaceground optical communication was established. Using the simulation system, the highest communication rates as to the different atmospheric visibilities were analyzed, the assumptions that bit error rate is superior to 10－7, the minimum transmitter power and the maximum communication distance were discussed in order to achieve the communication rate to 1.5 GHz and bit error rate is superior to 10－7. The result indicates that influence of the atmospheric visibility to the bit error rate is more obvious, when the transmitter power is greater.