2D　van　der　Waals　(vdW)　heterostructures　as　potential　materials　for　solar　energy-related　applications　have　been　brought　to　the　forefront　for　researchers.　Here,　by　employing　first-principles　calculations,　we　proposed　that　the　PtS2/GaSe　vdW　heterostructure　is　a　distinguished　candidate　for　photocatalytic　water　splitting　and　solar　cells.　It　is　shown　that　the　PtS2/GaSe　heterostructure　exhibits　high　thermal　stability　with　an　indirect　band　gap　of　1.81　eV.　We　further　highlighted　the　strain　induced　type-V　to　type-II　band　alignment　transitions　and　band　gap　variations　in　PtS2/GaSe　heterostructures.　More　importantly,　the　outstanding　absorption　coefficients　in　the　visible　light　region　and　high　carrier　mobility　further　guarantee　the　photo　energy　conversion　efficiency　of　PtS2/GaSe　heterostructures.　Interestingly,　the　natural　type-V　band　alignments　of　PtS2/GaSe　heterostructures　are　appropriate　for　the　redox　potential　of　water.　On　the　other　hand,　the　power　conversion　efficiency　of　ZnO/(PtS2/GaSe　heterostructure)/CIGS　(copper　indium　gallium　diselenide)　solar　cells　can　achieve　similar　to　17.4%,　which　can　be　further　optimized　up　to　similar　to　18.5%　by　increasing　the　CIGS　thickness.　Our　present　study　paves　the　way　for　facilitating　the　potential　application　of　vdW　heterostructures　as　a　promising　photocatalyst　for　water　splitting　as　well　as　the　buffer　layer　for　solar　cells.