In the power system, although composite insulators are widely used, with the increase of operation time, the V-shaped insulator string has the problem of decay and fracture, which seriously threatens the transmission safety. In view of the fact that V-string insulators account for a relatively high proportion of the actual line decay defects, this paper focuses on the stress of the interface adhesive layer of the mandrel sheath under wind load. The COMSOL finite element model of the FXBW-500/300SCI composite insulator was established to analyze the stress of the adhesive layer under different wind speeds. The results show that the wind speed is positively correlated with the horizontal load, and the maximum stress of the adhesive layer increases from 0.6640 MPa to 2.090 MPa when the wind speed increases from 18 m/s to 42 m/s. The performance of the adhesive layer is acceptable at low wind speed, and the risk of deterioration and fracture increases dramatically at high wind speed. At the same time, the unique mechanical characteristics of the V-string (tension on the windward side, stress conversion on the leeward side, and possible buckling instability under extreme winds) caused continuous damage to the adhesive layer. This study provides a key basis for understanding the chipping mechanism of V-string insulators and ensuring the stability of transmission lines, and is helpful for optimizing the anti-chipping design and operation and maintenance strategies of insulators.