A tunable femtosecond optical parametric oscillator is designed and built, and the signal light stability with different cavity lengths is studied. The output stability is improved by the method of power and wavelength locking respectively, and the cavity length is controlled by the proportional-integral control system. The effects of the two methods on improving the signal optical output power and spectral stability are compared. The output wavelength of the oscillator can be tuned from 1317 nm to 1610 nm. The standard deviation of signal output power and wavelength is promoted to 0.16% and 0.35% by using the power stabilization method over a period of 15 min, and to 0.25% and 0.03% by using the wavelength stabilization method over the same period of time. It proves that both the power stabilization method and the wavelength stabilization method are sufficient for output stability in optical parametric oscillator. The requirement of power stability and wavelength stability for the output signal of femtosecond optical parametric oscillator varies from different applications, this work compares and studies the locking effects of two locking methods, and provides experimental basis and reference for future research.