【Objective】The fertilization of the fern Lygodium japonicum are observed 【Methods】using electronic. 【Results】The results indicated that: ① Lygodium japonicum do not have the typical egg envelope and fertilization pore, and spermatozoa penetrates the egg through the pore region. ② The first spermatozoon entered the cytoplasm of the egg, and 2-6 spermatozoa could also pass through the pore region to enter the fertilization cavity below the pore region of the egg, but could not fuse with the egg cytoplasm. ③ After the sperm enters the egg, the fertilized egg shrinks markedly to prevent the entry of other sperm, and a membrane structure is formed at the location of the pore region above the fertilization cavity, which also plays a role in blocking the entry of other sperm into the fertilization cavity. ④ Nuclear fusion was initiated 30 min after spermatozoa entered the egg cell. The nucleus of spermatozoa was initially concentrated at one end of the egg nucleus and gradually penetrated into the nucleus of the egg, and nuclear fusion continued as the fertilized egg expanding. ⑤ Around 10 h after fertilization, the zygote produces a large number of vesicles, which first establish horizontal polarity and then change to vertical polarity, and undergo the first division of the zygote. 【Conclusion】When Lygodium japonicum undergoes fertilization, spermatozoa enter from the pore region and produce a fertilization cavity, which is similar to the core leptosporangiatae.