Two phase delay elements λ/4 wave plate QWP and λ/2 wave plate HWP are used in the system of phase-change two beam optical head. The characteristes of QWP greatly affect the feature of the system, including signal to noise ration (SNR)of reading signal of optical disk and quality of servo signal. In this peper the defects of conventional wave plate is analyzed, and the design consideration of a wave plate with titling optical axis are mainly discussed.