In　order　to　improve　both　performance　and　stability　of　perovskite　solar　cells,　a　design　is　provided　by　combining　the　advantages　of　high-efficiency　3D　perovskite　solar　cells　(PSCs)　and　long-term　stability　2D　PSCs.　A　2D/3D　hybrid　perovskite　film　with　a　dual　(bulk-　and　surface-)　passivation　approach　is　realized,　based　on　in-depth　discussion　of　the　guanidine　halide　(GuX)　passivation　mechanisms.　The　approach　can　reduce　the　charge　carrier　losses　in　the　bulk　and　prevent　decomposition　at　the　surface.　Based　on　a　combination　of　ab　initio　molecular　dynamics　simulations,　Urbach　energy,　and　photovoltage　measurements,　it　is　indicated　that　the　engineered　components　of　GuX　salts　are　GuCl　for　bulk　treatment　and　GuI　surface　treatment,　respectively.　The　former　can　lower　the　nonradiative　recombination,　and　the　latter　can　prevent　the　halogen-out.　Moreover,　drive-level　capacitance　profiling　is　employed　in　the　context　of　the　2D/3D　perovskite　structure　for　revealing　and　proving　the　passivation　mechanism.　The　2D/3D　hybrid　perovskites　achieve　long-term　stability　(efficiency　degradation　＜10%　after　30　days　without　encapsulation)　and　significant　enhanced　efficiency　(22.53%)　compared　with　the　efficiency　(20.31%)　of　the　control　device.　This　work　represents　a　rational　design　strategy　for　bulk　and　surface　passivation　treatment　in　2D/3D　hybrid　perovskites.