Abstract: The coiled tubing of a high-temperature and high-pressure gas well in a western oilfield fractured during the downhole process. Macroscopic observation, non-destructive testing, chemical composition analysis, mechanical performance test, metallographic inspection, scanning electron microscopy and energy spectrum analysis were used to analyze the cause of coiled tubing fracture. The results showed that during the downhole process of coiled tubing, wax formation occurred on the pipe wall. The coiled tubing was subjected to a compressive load, which caused the downhole to be blocked. When the compressive load exceeded the yield strength of the material, the coiled tubing was compressed and deformed and subsequently fractured.