Abstract. Satellite measurements during April to June in 2019 and direct observations from 28th to 30th May in 2019 about the Kuroshio Extension Front are conducted. The former shows the front experience a process of stable-unstable-stable state caused by the movement of the Kuroshio Extension’s second meander and a pinched-off eddy. The latter indicates the steep upward slopes of the isopycnals tilt northward in the strong frontal zone as well as several over 100 m thick blobs of cold and fresh water in the salinity minimum zone of North Pacific Intermediate Water. Using isopycnal anomaly method and diapycnal spiciness curvature method, characteristic interleaving layers are shown primarily in σ_θ = 26.3–26.9 kg/m³, which corresponds to large variations of potential spiciness in intermediate layers. Further analysis indicates the development of thermohaline intrusions may be driven by the double diffusive instability and the velocity anomalies. Besides, we find the turbulence mixing attributed to symmetric instability and shear instability is very strong in intermediate layer.