The invention belongs to the technical field of wireless communication, and in particular a multi-user iteration soft detection device and method based on the optimal Bayesian. A free space laser communication transmission and receiving system mode based on the IDMA is adopted by the method, a signal is transmitted after being encoded by a forward encoder and interleaved and modulated by an interleaver at a transmitter, and then prior information of the received signal is updated by use of the optimal Bayesian multi-user soft detection algorithm through the ESE and DEC decoder in a receiver; the multi-user interference is reduced, and the iteration soft demodulation of the signal is realized. The device disclosed by the invention comprises two parts: the free space laser communication transmitter and the free space laser communication receiver based on the IDMA. The device has good inhibition effect to the multi-user interference, and can resist the impact from the atmosphere turbulence to some extent, and can be extensively applied to the high speed data transmission scene in the networking of the Internet of Things.