The vector tracking algorithm uses a single extended Kalman filter(EKF) to predict the time-delays and the Doppler deviations of the GNSS signal, while also estimating the user’s position, velocity, and clock state. In this paper, the effects of multipath on the tracking performance of the vector delay / frequency lock loop(VDFLL) is studied for better application in the multipath environment. The error expressions of the measurements are given in theory. The tracking error caused by multipath is reduced by VDFLL, which is proved by the tracking error of VDFLL through a new iterating method. The theoretical analysis is verified by the Monte Carlo simulation. The vector tracking algorithm uses a single extended Kalman filter (EKF) to predict the time-delays and the Doppler deviations of the GNSS signal, while also estimating the user’s position, velocity, and clock state. In this paper, the effects of multipath on the tracking performance of the vector delay / frequency lock loop (VDFLL) is studied for better application in the multipath environment. The error expressions of the measurements are given in theory. The tracking error caused by multipath is reduced by VDFLL, which is proved by the tracking error of VDFLL through a new iterating method. The theoretical analysis is verified by the Monte Carlo simulation.