Using the daily temperature data from 63 stations from 1971 to 2011 over Zhejiang Province, combining with the phenology data, statistical calculations and comparative analysis are conducted. The results show that the seasons often start later by the method of pentad temperature and earlier or later with the methods of meteorology and climatology; the abnormal season start dates caused by different methods exhibit different characteristics in various regions. The main reasons for the abnormal season start dates are analyzed, and the results indicate that abnormal cases occur mainly when the temperature fluctuation of several days leads to the unsatisfied conditions of season change, but the lasting time of the fluctuations is not long generally, mainly in 3 to 5 days, and the fluctuation range is not great. So considering fully the advantages and disadvantages of various methods and the influence of temperature fluctuation, a method is presented, which is reasonable relatively and applicable to Zhejiang Province and can solve the problems of these methods. The provincial average start dates of seasons are 16 March, 29 May, 30 September, and 8 December. The frequency of seasons starting earlier or later reduced obviously, compared with other methods，and the result is more in line with the phenology in each region.