Based on the survey of observation,the factors affecting prevalence degree of wheat scab( Gibberella zeae) were analyzed through coupling method. The results showed that the average diseased ear rate before harvest( disease index) was associated with the average relative humidity from April to early May,the average temperature from April to early May,and the interval from peak maturity stage of perithecium to full heading stage of wheat. The interval was used to measure the coincidence degree between release period of ascospore and ear period( heading to grouting stage). The prevalence of wheat scab was determined by coincidence degree and meteorological conditions of ear period. Quantitative prediction should be conducted,to improve prediction and control levels.