Abstract: Both the Voyager 1 and the Cassini spacecraft had close encounters with Titan, and detected that the ions distribute asymmetrically between the Saturn-facing and the anti-Saturn facing sides of Titan's wake. In this paper the trajectories of ions born in Titan's exosphere are simulated through a simple model. The results show that the heavy ions have gyroradii comparable with Titan's radius but the light ions' gyroradii are not so large. Because of the finite gyroradius effects, most of the heavy ions on the side toward Saturn are absorbed by Titan's atmosphere. Therefore the densities of ions on the two sides of Titan's wake are asymmetrical. This asymmetry makes the wake unbalanced and deviate from the corotation direction. Through the mechanics equilibrium of the wake it is found that the wake will deflect toward Saturn by about 19o from the corotation direction. This is consistent with the observation of the Voyager 1.