Abstract A 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 n e ( 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.