DFT calculations have been performed to explore the defective structures and oxidation properties of Janus AsP. By comparing the structural stabilities of these defective structures, the SW-I possesses the smallest formation energy of only 0.103 eV, which is easy to form on the Janus AsP surface, while DV-555777 defects have relatively high formation energies due to the larger structural distortion. The SV defects induce the electronic defect states near the Fermi level, but SW and DVs defects do not. Different from BP, where the O2 molecule will dissociate spontaneously on its surface, the dissociation of O2 molecule on Janus AsP needs to overcome a large barrier, i.e., 0.98 eV for SW-I and 0.93 eV for SV-5566-I. Our work has indicated that the Janus AsP possesses better oxidation resistance than BP, and even with surface defects, they provide wide applications in electronic and optical devices.