The effects of vacancy defects and noble metals (NM = Rh, Ru, Pd, Ag) on the structural stability, electronic structure, and magnetic properties of arsenene were investigated using a first‐principles study. Vacancy defects have a great influence on both the magnetic properties and the band gap of arsenene. With the decrease in defect concentration, the magnetic moment of the vacancy defect system can be increased, and the bandgap transition from metal‐direct–indirect can be realized. After NM adsorption of vacancy defect arsenene, we considered three defect concentrations. It was indicated that there was a large adsorption energy between NM and vacancy‐defective arsenene, indicating that the adsorption system was relatively stable while the change in defect concentration did not have a significant effect on charge transfer. Except for the Ag adsorption system, the defect concentration can effectively modulate the band gap of the adsorption system and make it exhibit various electronic structures, such as semiconductors and metals. In terms of magnetic properties, not all NM atoms can induce arsenene to appear magnetic. Except for the Ag adsorption system, the defect concentration can make the adsorption system exhibit a variety of magnetic properties. It can induce the magnetic state of vacancy‐defective arsenenes or lead to the disappearance of magnetism. The spin polarization of the adsorption system mainly originates from the NM atoms or As atoms around the vacancies.