In this paper, we study the throughput optimization problem of a CSMA network with imperfect sensing by considering both miss detection errors and false alarm errors. The analysis shows that the maximum network throughput of CSMA significantly drops as the miss detection probability increases, while is less sensitive to the false alarm probability and the number of nodes. To achieve the maximum throughput, the transmission probability of each node should decrease with the miss detection probability or the number of nodes, while increase with the false alarm probability. The maximum network throughput and the optimal transmission probability are both obtained and verified by simulation results.