Abstract: A method for estimating carrier parameters is proposed by using extended Kalman filter (EKF) when the amplitude of the received signal is unknown. In the method, the state vector of EKF is composed of the carrier phase, the frequency and the product of the signal amplitude and auto-correlation of PN code. Theoretical analysis illustrates that the method is essentially the joint estimation of amplitude-locked loop and phase-locked loop with variable gains. The closed-form expression of transform function and equivalent noise bandwidth are obtained. Numerical simulation shows that the method proposed can obtain the high accuracy of estimation and the short convergent time.