The initialization conditions have great effect on the reflectivity contrast and CNR of Ge 2Sb 2Te 5 phase change optical disk. It is indicated that the reflectivity contrast increases at low velocity, while decreases at high velocity, as the initialization power increases and the reflectivity contrast decreases as the initialization velocity increases. Also the reflectivity contrast is very different when the measurement wavelength changes from 400 to 900 nm. The CNR of Ge 2Sb 2Te 5 phase change optical disk first increases and then decreases when the initialization power and velocity increase. The most favorable initialization conditions are those that power ranges from 1100 to 1300 mW and velocity ranges from 3.0 to 4 2 m/s.