Digestion of fly ash for agricultural use by heating with microwave was studied for the spectrophotometric method of boron determination, and the effective analysis approach was established. The results showed that: The sample could be digested completely in 25 minutes, the relative standard deviation ranged from 5.38% to 7.3% and the recovery from 94% to 109%. It proves that microwave digestion-spectrophotometric method for determining boron in fly ash is rapid, accurate and less environmental contamination method.