The daily precipitation data of Kunming Station for nearly 30 years from 1991 to 2020 were used to calculate the beginning and ending periods of Kunming rainy season （May-October）， further determine the length of the rainy season in Kunming.Additionally， statistical yearbook data for Yunnan Province and Kunming City were used， including year-end total population， urban built-up area， urbanization rate， per capita GDP， and other urban development factors， to determine the urban development process in Kunming.This process divided Kunming's urban development into a slow period （1991 -2003） and a fast period （2004 -2020）.The characteristics and differences in the length of the rainy season in Kunming City during these two periods were then analyzed and compared.Various analytical methods， including statistical analysis， wavelet analysis， and Mann-Kendall （M-K） mutation test， were employed to systematically analyze the temporal changes in the length of the rainy season in Kunming City.Additionally， the grey correlation analysis method was used to assess the correlation between the length of the rainy season and urban development in Kunming City.The results indicate that from 1991 to 2020， the start date of Kunming City's rainy season gradually became later， while the end date gradually became earlier， resulting in an overall trend of the rainy season getting shorter.Wavelet coefficient analysis revealed that there was no obvious regularity in the variation of the rainy season's length on time scales below 8 years， but on a 17-year time scale， there was a noticeable cycle of short-long-short-long-short variations， The rainy seasons from 2003 to 2008 and from 2014 to 2017 were relatively long， while the rainy seasons from 1991 to 2002， 2009 to 2012， and 2018 to 2020 were relatively short.The unclosed contour lines from 2018 to 2020 indicate a further trend of shortening.The M-K test showed that the length of the rainy season in Kunming City experienced four abrupt changes between 1991 and 2020， Occurring in 2002， 2008， 2012 and 2017.Regarding the relationship between Kunming's urban development and the length of the rainy season， the variation trend of the rainy season length during the slow urban development period remained relatively stable.However， after 2004， during the rapid urban development period， there was a significant reduction in the length of the rainy season in Kunming City， Extreme volatility became more pronounced as the urban development process accelerated.The SPSS （Statistical Product and Service Solutions） was used to predict the duration of rainy season in the next 10 years in Kunming City， The results show that the rainy season will continue to be shorter in the next 10 years in Kunming.When the grey correlation resolution was set at 0.5， four factors representing the urban development process had varying degrees of influence on the length of the rainy season in Kunming City， with correlation coefficients all exceeding 0.70， the results show that there is a significant correlation between the urban development and the length of rainy season in Kunming.Among these factors， the most influential one was the year-end total population， while the least influential was per capita GDP， with grey correlation coefficients of 0.88 and 0.70， respectively， signifying a high and significant correlation.The order of correlation coefficients for the four factors is as follows： year-end total population > urbanization rate > urban built-up area > per capita GDP.