Chlorophyll-a (Chla) concentration serves as a crucial indicator of marine phytoplankton biomass, reflecting the richness and diversity of marine ecosystems. Satellite remote sensing technology offers significant advantages in monitoring the spatiotemporal distribution of large-scale Chla concentration across global ocean waters. Using MODIS Chla concentration data from the past two decades (2003-2022), this study analyzed the spatiotemporal variability and trends of Chla concentration in the global ocean. Additionally, the relationships between Chla changes and MODIS Sea Surface Temperature (SST), the El Ni?o Southern Oscillation Index 3.4 (ENSO3.4), and the Indian Ocean Oscillation (IOD) were examined. The results indicated the following: (1) Spatially, Chla concentration was generally higher in coastal waters compared to offshore waters, with the lowest concentrations observed in deeper waters (less than 0.03 mg/m3). Seasonally, Chla concentration exhibited significant variation, with nearshore waters showing more pronounced seasonal changes than offshore waters. (2) In the open waters of the Pacific, Indian, and Atlantic oceans, the trend of Chla concentration remained relatively minor. However, Chla concentration showed an increasing trend in the majority of nearshore waters. (3) The month with the maximum monthly average Chla concentration varied in a band-like pattern with latitude. (4) Generally, Chla concentration and SST exhibited a significant negative correlation (p < 0.05) in global low-latitude regions (between 40°S and 40°N), while a positive correlation was observed in high-latitude sea areas. The correlation between Chla concentration and ENSO3.4 and IOD also displayed significant seasonal variations, indicating that ENSO3.4 and IOD factors have different impacts on Chla concentration variations in different sea regions.