Pulse laser action of a-axis YAP crystal with an activator concentration of 1 at% Er3+ ion has been studied. Two spectral lines at 1.655μm and 1.6623μm can oscillate simultaneously in this laser. Both spectral lines are linear polarization beams with polarized directions parallel to erystallographie B and C axes respectively. The output energy curve and time habit of oscillation for both emissions are also given. 103.7mJ output energy at 1.66μm has beea achieved from φ5×75mm Er3+:YAP rod with a laser threshold of 28J.