Objective To explore the significance of the formation of joint fluid in the joint cavity for the diagnosis of bone and joint diseases. Method Through retrospective analysis of 660 cases of joint cavity fluid in our hospital from 2017 to 2018, the common formation of joint cavity fluid was observed by ordinary light microscope and polarized light microscope. ResultAmong 261 patients with gout, 192 of 660 patients with joint effusion were diagnosed as urate crystals or urate phagocytes. The positive rate was 73.56% Calcium pyrophosphate crystals were detected in 8 cases, lupus cells in 3 cases, Wright cells in 32 cases, bacteria or bacteriophages in 8 cases, fat droplets in 18 cases, orange blood crystals in 3 cases. Conclusion The examination of the constituents of joint effusion can provide important clues and strong evidence for the early diagnosis of joint diseases reasonably, quickly and accurately. Urate crystals or calcium pyrophosphate crystals can be found in joint effusion as an important basis for the diagnosis of crystalline arthritis. Orange blood crystals found in joint effusion can be used to indicate obsolete hemorrhage. Persistent hemorrhage can be considered if accompanied by intact red blood cells. The presence of phagocytic bacteria in joint effusion can provide important clues for the diagnosis of bone and joint infections.