Mixing　helium　and　argon　as　the　working　gas　of　cold　plasma　jet　is　expected　to　combine　the　advantages　of　helium　plasma　jet　and　argon　plasma　jet.　Surface　distributions　of　ROS　on　model　tissue　treated　by　a　He+Ar+O2　plasma　jet　were　investigated　in　this　study.　The　results　show　that　the　effective　treatment　area　of　He+Ar+O2　plasma　jet　on　model　tissue　increases　with　the　argon　volume　fraction　in　the　working　gas.　When　the　argon　volume　fraction　was　60%,　the　effective　treatment　area　of　the　He+Ar+O2　plasma　jet　is　9　times　greater　than　that　of　the　He+O2　plasma　jet,　and　the　surface　distribution　uniformity　of　ROS　on　model　tissue　is　even　greater　than　that　of　Ar+O2　plasma　jet.　Furthermore,　mixing　helium　and　argon　as　the　working　gas　of　the　plasma　jet　diminishes　the　effect　caused　by　variations　in　the　treatment　angle　of　the　plasma　jet,　maintaining　the　effective　treatment　area　of　the　plasma　jet　directly　below　the　jet　nozzle.　These　results　suggest　that　He+Ar+O2　plasma　jet　is　advantageous　for　precisely　controlling　the　dosage　of　ROS　in　clinical　applications.　　©　2024　IEEE.