[Aim]  Osmia excavata is one of the most important pollinators in China, playing a crucial role in the pollination of fruit trees in the northern regions of the country. The pupal stage is a critical period for the formation of tissues and organs, growth, and development, and reproductive system maturation in adults. This study aims to investigate the developmental duration, morphological traits, reproductive organs, and the body mass of O. excavata during the pupal stage. [Methods]  The cocoons were carefully extracted and bees sharing the same compound eye color were dissected in the laboratory for analysis. [Results]  The results showed that the color of the compound eye of O. excavata changed significantly during the pupal stage, transitioning from pink to brown, brown to black, before ultimately becoming black. The average duration of the transition in eye color of O. excavata pupae was (7.00±0.13) d from pink to brown, (6.57±0.17) d from brown to brown-black, and (7.13±0.21) d from brown black to black. The average duration from a black-eyed pupa to the development of a black head and thorax was (8.54±0.24) d. The primary transformations seen during the pupal stage included changes in the compound eye color, external morphological structure, body surface color, and ovary and testicle structures. The weight of female bees is significantly more than male bee when the color of the compound eye turned black (P < 0.01), the female bee is larger, the end of the abdomen is more sharp, there are prominent oviposition petals, the two ovaries are symmetrical, and each ovary has three ovarian tubes; The male bee is small, the end of the abdomen is relatively round and blunt, there is no bulge, the left and right of the sperm nest, merge into a “Y” shape, and the sperm nest and ovary are white and transparent. [Conclusion]  The pupal stage of O. excavata undergoes significant internal and external changes during development. As it develops from the pre-pupa to the adult stage there is a gradual development of the internal tissues and organs, as well as changes in the external morphology. Our research investigated developmental duration and morphological changes during the pupal stage of O. excavata. We identified differences in morphological traits, body mass, and the morphology of ovaries and testes between females and males throughout this phase. Our findings establish the foundation for comprehensive research into organ growth, differentiation, and development in the solitary wasp, O. excavata.