The material composition of geological samples is very complicated. Generally, the method for accurately determining trace elements in geological samples needs to digest the solid samples into liquid state, which is convenient for inductively coupled plasma mass spectrometry. The previous digestion method takes a long time and the operation process is complicated. The Ultra CLAVE microwave digestion instrument was used to digest the geological samples. The types and dosages of the acid used for digestion and the optimal conditions for instrumental testing were published. The results show that this method has short processing time, small data error, safer operation and good digestion effect. This method is suitable for geological sample analysis.