During measuring the content of potassium in compound fertilizer by potassium tetraphenylborate gravimetric method，the general electric hot plate heating technology used in handling the sample had some disadvantages of time consuming and energy consumption, therehy further affecting rapid analysis. In this research, the microwave heating technology, which was characterized as fast dissolvement and drying, was used for measuring the content of potassium oxide in compound fertilizer. The experimental results demonstrated that the electric hot plate heating method could be replaced by microwave heating. With high temperature for 5 minutes to dissolve the sample, and the accurate drying time was 12 minutes. Also, the precision and addition standard recovery rate (99.66%～100.58%) of the method met the requirements respectively. The method reduced the analysis time by one hour and a half and saved the energy by 60%～70%,improved efficiency,quality and stability of production.