Using the data of 3 consecutive rainfall days and no rain days during mid September to early October in near 50 years (1961-2009) from 12 representative stations in major apple cultivating counties of Shaanxi, the index of continuous rainfall days (ICRD) has been designed and calculated, and is divided into the strongest, stronger, medium, weak and weaker five levels, on the basis of which, conducting the independent sample trial by using typical K order autoregressive AR (K) forecasting model. The basic result of this research is that the ICRD could objectively reflect the intensity of continuous rainfall days in apple maturity period. In addition, the typical K order autoregressive forecasting model has about 83% forecasts being accurate or basically accurate, indicating that the effect of this forecasting model is still good and of practical value.