By filtering the Doppler velocity of S-band weather radar, the wind radial velocity deviation caused by biological directional migration is obtained, which can effectively distinguish the cross-sea migration activities of directional migratory organisms. The results show that the low-pass filtering of radar Doppler velocity at the same range can effectively separate the directional migratory organisms from the clear-sky echoes generated by undirected plankton and atmospheric turbulence. It also can realize the monitoring of the directional migratory organisms’ cross-sea migration activities, and provide the data of their migration paths in the process of migration. In order to verify the algorithm, through the verification of a biological migration process of the US KICT radar over the night of 30 September 2012, the successful seperation of the birds, which is migrated from the insects, was successfully relied on the Doppler velocity and reflectivity factors. According to the artificial observation results of Changdao Pest Control Field Scien-tific Observation Station, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, the radar data analysis of the night migration period of armyworm in the Bohai Strait on 30 May 2017 shows that this method can effectively identify and monitor the activities of orientated migrating organisms over the Bohai Strait.