Abstract: To avoid the burst of some component parts of UF_6 cylinder is a vital subjectduring operations in both laboratories and industry. In this work the bursting reasons were studied by the aid of the phase diagramand Clausios-Clapeyron equation. The results showed that two reasons are respon-sible for the burst. First, the temperature is above the triple point. Second, thefilling factor of solid UF_6 is too high. It is suggested that operators should be familiar with the characteristics ofUF_6. That temperature should be kept below 64℃ and that the filling factorsolid UF_6 should not exceed 50 percent.