AbstractA six-channel FIR laser interferometer system, which is used to measure the electron density profile, has been developed on the HL-1. device. The interferometer used a HCN laser with output power of about 60 mW. Using this interferometer, the temporal evolution of the density profile ne (r, t) has been obtained and analyzed using various experiments during ohmic discharge in the HL-1 tokamak. The phase accuracy of the interferometer is about π/8.