The influence of the tilting of the photorefractive hologram grating on wavelength demultiplexer is studied. An effective method, which can predict the influence of the grating tiling on the demultiplexing performance, is presented in order to avoid the unnecessary experimental spending. The phase error caused by the tilting of the Bragg grating is corrected with a Fourier analysis. The spectral response of the demultiplexer is calculated by using a rigorous coupled wave analysis method. The influence of the tilting of the Bragg grating on the spectral response is analyzed. It is shown that the phase difference due to the tilting of the grating can result in a large insertion loss and a large crosstalk. It is pointed out that the hologram tilting must be avoided as much as possible since it deteriorates the final performance seriously when a photorefractive hologram Bragg grating is used for wavelength demultiplexing. The experimental method of the grating image processing is also introduced in the paper. The experimental results accorded with theoretical computation commendably by testing the spectral responses of two demultiplexers with the tilting gratings.