With an enhanced photoacoustic cell, the surface loss of the cell is decreased obviously, thus the resonant peak broadening is mainly due to the vibrational-translational (V-T) relaxation of AsH3. The high quality factor Q value of 374 has been achieved for AsH3 gas at the pressure of 9.06 kPa. An expression for acoustic wave amplitude as a function of modulation frequency and relaxation time has been derived. This theoretical formula is fitted to the experimental data, then the relaxation process of AsH3 is studied . The results reveal that the V-T energy transfer of gas molecules is determined mainly by the molecules′ vibrational states, which contribute the most to the vibrational heat capacity; and the two-energy level double relaxation process is the most possible process for the vibrational-translation energy transfer for AsH3.