Advancements in laser decoy techniques have rendered laser semi-active guided weapons using traditional encoding methods unable to fulfill the needs of modern warfare. A fusion guidance system based on multiple sub-beam interference is proposed. The spatial “watermark cipher code” is combined with the temporal coded signal to produce a new temporal-spatial watermarking coded signal. The laser is divided into several equal power sub-beams which can produce an effective spatial watermarking interference pattern due to their coherence. Calculation results show that the interference pattern presents special distribution features of alternating brightness and darkness. The operating range and the identification of the guidance system are enhanced by the watermark encoding mode. When the position offset and angle deviation of the beam splitter, in the multiple sub-beams coherent emission system are less than 0.1λ(λ is the wavelength) and 0.1θ0(θ0 is the beam divergence), respectively, the effect of mechanical vibration on the emission system can be ignored.