The high frequency (HF) PO/GO computation based on ray tracing approach is presented to fast compute the EM scattering from arbitrary dielectric target with electric- large size. For lossy medium, the generalized Snell-Descartes and Fresnel laws are introduced to determine the propagation direction of equi-phase and equi-amplitude plane of reflection and refraction wave, which is the main difference from the classical ray tracing approach. The GO reflection and refraction rays are traced according to the propagation direction of equi-phase surface step by step. Accompany with the wave propagation, the phase delay is computed along the normal direction of equi-phase, and the energy attenuation is computed along the normal direction of equi-amplitude. On the exiting surface, the PO integration of surface field is considered for outgoing field computation. For lossy dielectric surface, the PO surface field is inhomogeneous, and this paper derives an analytical integral formula for arbitrary triangular patch to avoid the numerical integral on the dense meshing of 1/8 wavelength. In numerical simulation, the target is constructed with triangular dielectric patches according to its geometry CAD model, not need to mesh according to the electric wavelength. Several models, such as multi-layer dielectric plate, dielectric coating plate, lossy dielectric cubic, et al., are used for validation and comparison with FEKO software, taking the requirements of memory and CPU time into consideration. The numerical simulation indicates that the new HF method is valid and efficient for electric-large target with arbitrary dielectric medium.