Abstract: Drill core analysis is a necessary preliminary study to explore oil and gas field. This kind of drill core always contains high contents of K (12.30 mg/g), Na (15.04 mg/g), Al (28.83 mg/g) and Fe (11.13 mg/g) with large amount of organic matter. This is the first time that the method of decomposing organic matter in the drill core by microwave digestion with concentrated HNO₃ and H₂O₂, and dissolving the silicates by HCl and HF acids has been used. The elements of K, Na, Ca, Mg, Al, Fe, Mn and Ba were measured by using atomic absorption spectrometry. The linear correlations of standard curves were obtained (r=0.9949-0.9998) and recovery factors were between 92.2%-101.6%. This method of microwave digestion has advantages of no sample loss, simple operation, less usage of reagents and is environmentally friendly, as well as being accurate, reliable and having a low detection limit.