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A fiber-optic interferometer based on fringe projection and sinusoidal phase modulation for three-dimensional surface profile measurement is presented.It makes use of Youngs double pinhole interference principle to achieve fringe projection.And sinusoidal phase modulation is accomplished by driving piezoelectric transducer using a cosine voltage single.To eliminate the external disturbances such as mechanical vibration and temperature fluctuation,we propose a phase control system by detecting the phase drift and giving real-time compensation.We reduce the phase error to 6.8 mrad and accomplish the phase stability of the interference fringe.By measuring the surface profile of a glass plate for two times over an interval of 10 min,the repeatability is about 12 nm.The experimental results show that the proposed interferometer can be used for surface profile measurement with a high precision.