Abstract: Global climate change is inducing observable shifts in vegetation phenology, with spatial heterogeneity in both trends and drivers. As an important ecological barrier in the upper reaches of the Yellow River, the forests in the Huangshui River Basin remain under-researched regarding phenological responses to climate change. This study was conducted on the Google Earth Engine (GEE) cloud platform, utilizing MODIS vegetation index time-series data and meteorological data, along with the "one map" of forest land in the Huangshui River Basin. It applied multiple analytical methods, including double logistic function fitting, Theil-Sen trend analysis, Mann-Kendall significance tests, and partial correlation analysis, to examine the spatiotemporal distribution patterns, change trends, and seasonal climate responses of forests and dominant tree species phenology in the Huangshui River Basin from 2000 to 2020. The results show that: (1) the average start of growth season (SOS), end of growth season (EOS), and length of growth season (LOS) for forests in the Huangshui River Basin are on Day 143, Day 261, and 120 days, respectively. The SOS of forests changed distinctly, showing an overall trend of earlier onset, advancing at a rate of 0.080 d·a^-1. In contrast, the EOS and LOS of most forests exhibited only slight changes. (2) Among dominant tree species, cypress tree display the most pronounced phenological changes, with SOS advancing at a rate of 0.237 d·a^-1, EOS delaying at a rate of 0.211 d·a^-1, and LOS prolonging at a rate of 0.403 d·a^-1. (3) The advance of SOS is primarily influenced by the land surface temperature (LST) in the spring of the current year and the winter of the previous year, while the delay of EOS is mainly affected by the precipitation in the summer and autumn of the current year. Additionally, an increase in summer LST can accelerate the onset of EOS.