In order to develop Onchidium struma's artificial aquaculture technology and meet the growing market demand, it is crucial to know O. struma's spawning law very well. This study investigated the spawning characteristics within three years and comparatively studied the relationship between spawning and astronomical tides. During three years, O. struma in the same regions was obtained from July to September from 2013 to 2015, and the spawning was recorded each time. After that, the spawning and tidal height was comparatively analyzed. The results showed that O. struma spawned mostly at the neap tide (7^th, 23^rd) every month, and this spawning could last 6-7 days by lunar calendar. The spawning stopped at the advent of 1-2 days before the next spring tide, while the tide would take O. struma larva hatched into the ocean. After about 15 days' development in the sea, O. struma developed into the big veliger and then came back to the beach along with the next tide. It can be concluded that:(1) O. struma spawning rules were related to the tide which showed a peak spawn within the neap tide and reached peak 2-3 days after spawn. (2) Theoretically, it takes 14 d 19 h 55 min from one neap to another neap theoretically. However, in fact, O. struma's spawning cycle was 14 d 21 h 20 min because of the tidal hysteresis.