Nowadays, secondary batteries based on sodium (Na), potassium (K), and magnesium (Mg) stimulate curiosity as eventually high-availability, nontoxic, and eco-friendly alternatives of lithium-ion batteries (LIBs). Against this background, a spate of studies has been carried out over the past few years on anode materials suitable for post-lithium-ion battery (PLIBs), in particular sodium-, potassium- and magnesium-ion batteries. Here, we have consistently studied the efficiency of a 2D alpha-phase arsenic phosphorus (alpha-AsP) as anodes through density functional theory (DFT) basin-hopping Monte Carlo algorithm (BHMC) and ab initio molecular dynamics (AIMD) calculations. Our findings show that alpha-AsP is an optimal anode material with very high stabilities, high binding strength, intrinsic metallic characteristic after (Na/K/Mg) adsorption, theoretical specific capacity, and ultralow ion diffusion barriers. The ultralow energy barriers are found to be 0.066 eV (Na), 0.043 eV (K), and 0.058 eV (Mg), inferior to that of the widely investigated MXene materials. During the charging process, a wide (Na+/K+/Mg2+) concentration storage from which a high specific capacity of 759.24/506.16/253.08 mAh/g for Na/K/Mg ions was achieved with average operating voltages of 0.84, 0.93, and 0.52 V, respectively. The above results provide valuable insights for the experimental setup of outstanding anode material for post-Li-ion battery.