There are scarce researches about the male reproductive system of Procambarus clarkii. This study aims to get some features of the male reproductive system of P.clarkii. The ultrastructure of the vas deferens was studied by using transmission electron microscopy, the microstructure of testis, vas deferens and spermatophore of P.clarkii was studied by using paraffin method, and the annual variation of the testis was investigated. Testis comprised many spermatogenic acini and collecting ducts whose structure is like grapes; The germ cells in the spermatogenic acini are transported to the vas deferens by through the collecting duct after matured; P.clarkii has a right and a left vas deferens, the right vas deferens was half longer than the left, the right vas deferens has a larger diameter, its curling degree and inclusion content are materially higher than the left, and secretory cells of the right vas deferens have more abundant endoplasmic reticulum. The vas deferens can divide into anterior, middle, posterior sections and a male gonopores acording to the difference of its morphous. Anterior and middle vas deferens can secrete materials for the formation of the spermatophore. The posterior section can store and ejaculate spermatophore. Male gonopores are the outcome of the vas deferens. The shape of spermatophore is elongated capsule or ellipsoidal. The spermatophore is composed of sperm mass, spermatophore matrix and two layers of spermatophore wall, sperm mass is in one side of the spermatophore. Male P.clarkii has two maturity periods that the most part of spermatogenic acini in the testis are at spermatid stage in its annual variation, and one is from May to August and the other is in October.