Urban green development is the internal requirement to achieve high quality development. It is the premise and basis of relevant research to evaluate the level of urban green development scientifically and grasp the spatiotemporal evolution characteristics of green development level. First, based on the panel data of 286 cities at prefecture level and above in China from 2003 to 2019, this study constructed the evaluation index system of urban green development level from three aspects including green production, green ecology and green living, to estimate the green development level of the Chinese cities. Second, this study reveals the spatial and temporal evolution characteristics of urban green development level by spatial correlation analysis, hot spot analysis, Dagum Gini coefficient decomposition and other methods. The following results are obtained. (1) The level of green urban development in China is steadily improving, but there is still much room for improvement. (2) The green production index, green ecological index and green living index increased year by year during 2003-2019, with average growth rates of 2.67%, 4.61% and 1.66%, respectively. The green ecological index contributes the most to the improvement of urban green development level, followed by the green living index. The green production index is the lowest, directly dragging down the level of urban green development. (3) The level of urban green development in China presents a typically positively spatial correlation with high-high agglomeration and low-low agglomeration. The hot spots are concentrated in the eastern coastal and central cities except Guangdong Province. (4) The overall, intra-regional and inter-regional differences in the level of urban green development in China show a downward trend. Among them, inter-regional differences are the main source of overall differences.