In order to study the development of the reproductive system of the "pre-pupa" and "pupa" of Didesmococcus koreanus Borchsenius, the morphological characteristics during the process from the 2nd instar nymphs to male adults were observed under the microscope (Olympus). The results showed that: the prepupal duration is 2-4 days, and the pupal duration is 4-6 days; The male reproductive system is composed of a pair of testis (T), a pair of vas deferens (vd), ejaculatory sac (es), ejaculatory duct (ej), and a pair of mesadenia (me). At different stages of development, the morphological structure of the male reproductive system of the D. koreanus was observed a series of changes. At the end of the 2nd instar nymphs, the apex of the T is enlarged and full of white content. In prepupal stage, the base of the T became thicker, the contents showed light and dark stripes, and the length of the vd and ej increased. The stripes in the T of the pupal stage disappear and the contents are gel-like. The T of the male adult became distorted, with a pointed end and enlarged base. The es of the male adult was enlarged and filled with white gelatinous spermatozoa.