Abstract: In this paper, the mesoscale eddies in the Northwest Pacific Ocean (0°—45°N, 120°—180°E) are automatically identified and followed by the method of OW parameter and closed curve. The seasonal variation, interannual variation, quantitative characteristics and geometric parameters of mesoscale eddies with different lifetime are analyzed. It is found that the peak of the number of short lifetime (15-30 days) and medium lifetime (30-105 days) mesoscale eddies is about 2-3 months later than the cold peak of the meteorological season. Different from other lifetime mesoscale eddies, for the medium lifetime mesoscale eddies, cyclonic eddies (33.9 cm/s) rotates faster than the anticyclonic eddies (16.9 cm/s), and medium lifetime mesoscale eddies’ seasonal variation is the most significant. Winter is more suitable for the occurrence and development of mesoscale eddies in the Northwest Pacific Ocean, and in terms of lifetime, it is more likely to develop into medium lifetime eddies. There are three obvious periodic changes (the first main cycle, the second main cycle and the third main cycle) in the monthly number changes in mesoscale eddies of different lifetimes. According to the time scale of different main cycles, their influencing factors may be sunspot activity, ENSO phenomenon and seasonal variation respectively. In terms of geographical distribution, the distribution of high frequency of mesoscale eddies with different lifetimes is not completely consistent. In terms of eddy’s amplitude, the medium lifetime mesoscale eddies have the largest amplitude (15-25 cm), followed by the short lifetime mesoscale eddies (15-20 cm), and the long lifetime mesoscale eddies has the smallest amplitude (10-16 cm). In terms of eddy’s radius, the average radius of long lifetime mesoscale eddies is bigger (20-30 km) only in the subtropical countercurrent area, whereas the average radius of medium and short lifetime mesoscale eddies is bigger (30-45 km) in the north of the study area. From the geometric parameters, the mesoscale eddies’ geometric parameter of Northwest Pacific Ocean is not the biggest in the middle of life. It reaches its first high value about the first third of its life, and then fell slightly, maintaining a stable value, until it rises slightly to the second high value in the last third of life, and then fell rapidly to zero.