Based on the birefringent effect of liquid crystal, a liquid crystal Fabry-Perot filter in simple structure is designed and fabricated. This device can be used in wavelength division multiplexing. The tunable characteristic of this device was analyzed and simulated; the formula of the relation between the liquid crystal refractive index modulation and the rotary angle of the liquid crystal molecule arose from the modulated voltage is got. The test of the fabricated tunable filter shows that the performance of the device is mainly affected by the alignment of the liquid crystal molecule and the parameter of the reflectors of the Fabry-Perot cavity, and the tunable characteristic is good for this kind of device with the nematic liquid crystal as the media in the Fabry-Perot cavity. The tunable range of the tunable filter covers the C band and the full width at half maximum (FWHM) could reach 0.8 nm, the experimental result was coincident with the design well.