The principle of Doppler spectra detected by HFSWR (high-frequency-surface-wave radar) is given by a nonlinear integral equation from which can be extracted ocean wave parameters. By linearization, the equation can be transferred into a first kind of Fredholm integral equation approximately and can be displayed in a quadratic form. Conjunction gradient (CG) method is proposed to solve the optimization problem. Non-negative restriction is introduced to improve the involved CG algorithm and fit to the priori knowledge so that the ocean wave parameter is non-negative. Validity and accuracy of the proposed method are demonstrated by numerical simulation with different noise levels at one site and two sites.