According to the effect of sound field distribution in an acousto-optic crystal on diffraction efficiency and optical fields, an apodization method was proposed to improve the laser heterodyne interferometric efficiency. By taking a TeO2 for a substrate, the effect of sound field distribution and volume grating contrast in an acousto-optic device on the diffraction efficiency was analyzed. A nonuniform contrast model was established and the apodization method was used to control the nonuniform distribution of the spatial sound field. The results show that when the radio frequency is tuned to a working range from 100 to 105 MHz for an Acoustic Optical Modulation(AOM) without apodization, the diffractive spot shows two peaks with nonuniform distribution, diffractive light contains crosstalks with much noise and diffraction efficiency is affected. The heterodyne signal power is -1.7 dBm. However, the apodization achieves a better diffraction efficiency and crosstalk suppression. The diffraction efficiency reaches the maximum 98%, transmission bandwidth has been 50% to 60% of the total diffraction bandwidth. The heterodyne signal power is 3.8 dBm. The measurement results indicate that the method can optimize transmission capacity, suppress the crosstalk and can improve the laser heterodyne interferometric efficiency by an IF heterodyne signal voltage gain of 11 dB.