In order to ensure the driver of landing boat to go into landing ship quickly by tracking the optical guidance signal all the time, the divergence angle of the optical guidance system must meet some requirements. Ship motion theory is applied to analyze the divergence angle of the optical guidance system on landing ship. Based on the yawing motion of landing ship under the fifth sea state level, we ascertain the lateral divergence angle α must be not more than 14°. Based on the swaying motion of landing ship under the fifth sea state level, we ascertain the longitudinal divergence angle β must be not less than 15°. Research results can provide some references for applying in engineering.