Using the improved characteristic coefficient method,the probability strength of maximum precipitation from a 2 hour period to 24 hour period in every county of Taian City are evaluated. Evaluation result shows that probability strength of the 24 hour maximum precipitation on a 50 years cycle,a 100 years cycle and a 200 years cycle in central region of Taian city are 159. 9mm, 175. 9mm and 191. 8mm respectively. The probability strength of the maximum precipitation is also evaluated from a 2 hour period to a 24 hour period on different cycles in other counties of Taian city.