Abstract: Mental elements play important roles in the scientific utilization of crop straw. There is currently no standard method for determination of metal elements in straw. This article investigated the effects of different pretreatments on the determination of K, Cu, Fe, Zn and Mg in Astragalus mongholicus reference material (GBW10028), corn straw, wheat straw and cotton stalk by atomic absorption spectroscopy. The experimental results showed that microwave digestion, dry ashing and wet digestion had significant differences (P<0.05) on the content of metal elements in Astragalus mongholicus reference material (GBW10028). Microwave digestion had a higher precision and accuracy than dry ashing and wet digestion. Microwave digestion had the same effect on determination of metal elements of Astragalus mongholicus reference material (GBW10028), corn straw, wheat straw and cotton stalk. Microwave HNO3 and microwave HNO3-H2O2 pretreatments had no significant difference (P>0.05), microwave HNO3 pretreatment was more stable than microwave HNO3-H2O2 and microwave HNO3-H2SO4 pretreatments. Microwave HNO3 pretreatment was a more accurate and simple method for the determination of metal elements in straw.