With the development of optical fiber communication, the photorefractive functional waveguie gratings are being widely utilized in a great variety of devices and systems. A novel two-beam holographic approach, including a space beam and a guided-wave beam, for fabricating a photorefractive grating on Ti:LiNbO3 channel waveguides is proposed. The theoretical analysis of the experiemntal results show that the approach is practical and effective. This approach can be also used for fabricating the surface-relief waveguide gratings. It is a flexible means to fabricate various functional gratings with a grating-period shorter than the half-wavelength of the exposure light and the chirped-grating.