In optical disk systems, a semiconductor laser is used to read out the data recorded on the disc. Since the laser is the first noise source, there are strictly rated values for laser's noise in various optical disk systems to ensure the normal operation of the system. Among different laser noises, the worst one is the optical feedback noise. The feedback light will disturb the longitudinal modes of the laser and induce huge fluctuation in Laser's output. In our work, we study the effect of optical feedback on Laser's modes and relative intensity noises under various driving current and chop temperature. We try to find out methods that can suppress the Laser's noise and try to give some suggestions for the design of disc driven. Some experiments about a commercialized optical disk driver are also reported as well.