Abstract: The northern boundary of Pinus massoniana is in the ecotone of subtropic and warm temperate zone in the south part of Henan Province, the P. massoniana forest is widely distributed in Huaiyuan Township of Tongbai County and Boshan State Forest Farm in Zhumadian Municipality which are located at the upper reaches of the Huaihe River. The characteristics of canopy gaps in the P. massoniana forests were surveyed, and the effect of gap size on soil seed bank, seedling properties and species diversity was analyzed. The results showed that the gap size in these P. massoniana stands was mainly small and medium in size with the average area of 462 m2. The gap size could affect the forest regeneration through the influence on soil seed bank the quality and quantity of the seedlings and species diversity. The forest might be better regenerated when the gap size was around 40-60m2, which did not necessarily mean to be beneficial to the regeneration of P. massoniana. It was proposed that suitable gap size should be formed in the forest management so as to maintain the natural regeneration of P. massoniana forest.