Based on diffraction theory and groove and land model with elliptical pits blue-ray disc, the energy distribution on exit pupil was investigated and tracking error signal was obtained by Differential Push Pull (DPP) method when focus spot scanning through the blue-ray disc. Furthermore, the influence of traditional square pits and elliptical pits disc radial tilt on tracking error signal was compared. Result shows that ultra-high density disc for 50 GB blue-ray disc is very sensitive to radial tilt. In order to make sure that the disk is read correctly, the allowable radial tilt angle should be less than 0.15o.