A method of controlling chaos in nondegenerate optical parametric oscillator (NOPO) is presented in this paper. The chaotic state of NOPO can be converted into periodic state by modulating the driving field and the reduced decay rate of the fundamental mode with a sinusoid wave. The numerical simulation results based on the Lyapunov exponent spectrum,phase portraits as well as time series show that there are different periodic states for the chaos of NOPO system corresponding to different modulating amplitude and modulating angular frequency only if the maximum Lyapunov exponent of the system is nonpositive.