A special type of mesoscale eddy train consisting of three subsurface-intensified anticyclonic and cyclonic eddy pairs was first observed in the northeastern South China Sea (NESCS) by a long-term mooring array.  The maximum swirl velocity (temperature anomaly) caused by these subsurface-intensified eddies (SIEs) was located at 200-400 m (500-700 m) with the magnitude exceeding 14 cm/s (0.4 °C). Horizontally, the SIEs generally propagated westward, and their propagation speed (Cp) and length scale were estimated to be ~4.9 cm/s and ~250 km, respectively. Vertically, both the velocity and temperature structures of the SIEs were found to tilt southwestward with increasing depth.  Given that the swirl velocity exceeded the propagation speed, the SIEs were highly nonlinear and could trap water mass within their velocity cores. Based on the radius and “trapping depth” (where Us=Cp) of the eddy core, we further estimated the volume of water trapped within the SIEs and found that it can cause an annual mean equivalent westward transport of 2.2 Sv in the intermediate layer (500-950 m).  By synthetically analyzing the mooring observations, altimeter data and Hybrid Coordinate Ocean Model (HYCOM) products, we suggested that the SIEs most likely originated from the western Pacific. This argument was confirmed by the observed phenomenon that the SIEs were accompanied by the occurrence of low-salinity North Pacific intermediate water in the NESCS.  Further energetics analysis demonstrated that after propagating into the NESCS, the SIEs got strengthened by draining energy from the baroclinic instability of the mean current.