A micro-Gal absolute gravimeter based on high-precision and high-stability heterodyne interferometer is presented. The distance measuring technology of the gravimeter is studied in detail. The experimental results of distance measuring for a free-falling motion show that the high-precision heterodyne interferometer described in this paper can meet the demand of a micro-Gal absolute gravimeter with relative uncertainty of 6.4*10^(-9). Moreover, the heterodyne interferometer is more stable than the Mach-Zehnder interferometer (MZI) which is widely used in present absolute gravimeters.