Abstract: The satellite blackbody equivalent temperature data is used to investigate the possible mechanism leading to the great error in process of track prediction. The results show that the existence of the mesoscale convective system (MCS) may account for it. By using the non hydrostatic WRF model, the Typhoon Fengshen (2008) is simulated in high-resolution for better understanding the impact of the MCS produced in the west and southwest of the typhoon. In this paper, the simulation is double nesting with the highest resolution of 6 km and the sum of 78 h integrated. The PV-ωpiecewise potential vorticity retrieval diagnostics is applied to quantitatively evaluate the impact of the MCS on typhoon movement. It is found that the mean wind of MCSs on the steering level can reach 20% of the typhoon steering wind. Investigation into the effect of the MCS is also done by considering the MCS existence as an initial-value problem. Three model experiments were conducted and the results show that whether the MCS makes the typhoon turn left or right varies dependently on the direction of the typhoon steering flow and it also shows that the existence of MCS makes the typhoon go farther to the northwest in this case. Two different types of MCSs were investigated and it shows that stable relative position between the MCS and Typhoon Fengshen may be the reason why the MCS has great effect on the track of typhoon.