For the self-interference cancellation technology of in-band full-duplex underwater acoustic communication,the self-interference cancellation method in analog domain or digital domain is usually used to erase the self-interference signal. However,due to the problem of hardware equipment,the self-interference cancellation performance has an upper limit. The self-interference cancellation in spatial domain is often completed by sound absorption barrier or directional transducer. In this way,the upper limit of self-interference cancellation is increased, but the engineering application is more complicated. Also,this method has equipment dependence and limited cancellation capability. In order to further increase the upper limit of self-interference cancellation and reduce the complexity of self-interference cancellation method in spatial domain,this paper intends to complete self-interference cancellation in spatial domain based on array signal processing technology,and designs a beamformer aiming at the particular problems in in-band full-duplex underwater acoustic communication. The spatial filtering is used to weaken the self-interference signal and enhance the desired signal. The practicability and cancellation effect of this method have been verified by simulation and pool experiments.