The area of Arctic sea ice has dramatically decreased, and the length of the open water season has increased; these patterns have been observed by satellite remote sensing since the 1970s. In this paper, we calculate the net primary productivity (NPP, calculated by carbon) from 2003 to 2016 based on sea ice concentration products, chlorophyll a (Chl a) concentration, photosynthetically active radiation (PAR), sea surface temperature (SST), and sunshine duration data. We then analyse the spatiotemporal changes in the Chl a concentration and NPP and further investigate the relations among NPP, the open water area, and the length of the open water season. The results indicate that (1) the Chl a concentration increased by 0.025 mg/m3 per year; (2) the NPP increased by 4.29 mg/(m2·d) per year, reaching a maximum of 525.74 mg/(m2·d) in 2016; and (3) the Arctic open water area increased by 57.23×103 km2/a, with a growth rate of 1.53 d/a for the length of the open water season. The annual NPP was significantly positively related to the open water area, the length of the open water season and the SST. The daily NPP was also found to have a lag correlation with the open water area, with a lag time of two months. With global warming, NPP has maintained an increasing trend, with the most significant increase occurring in the Kara Sea. In summary, this study provides a macroscopic understanding of the distribution of phytoplankton in the Arctic, which is valuable information for the evaluation and management of marine ecological environments.