Currently,　energy　and　environmental　problems　are　becoming　more　serious.　The　use　of　solar　energy　to　split　water　and　produce　clean,　renewable　hydrogen　as　an　energy　source　is　a　feasible　and　effective　approach　to　solve　these　problems.　As　the　most　promising　semiconductor　material　for　photocatalytic　water　splitting,　TiO2-based　nanomaterials　have　received　increasing　attention　from　researchers　in　academia　and　industry　in　recent　years.　This　review　describes　the　research　progress　in　the　theoretical　calculations　of　TiO2-based　photocatalysts　in　water　splitting.　First,　it　briefly　introduces　some　commonly　used　theoretical　calculation　methods,　the　crystal　structure　of　TiO2　and　its　photocatalytic　mechanism,　and　the　principle　of　doping　and　heterojunction　modification　to　improve　the　photocatalytic　performance　of　TiO2.　Subsequently,　the　adsorption　state　of　water　molecules　with　different　coverages　on　the　surface　of　TiO2,　the　rate-limiting　steps　of　the　splitting　of　water　molecules　on　the　surface　of　TiO2,　and　the　transfer　process　of　photogenerated　current　carriers　at　the　interface　between　water　molecules　and　TiO2　are　analyzed.　In　addition,　a　brief　review　of　research　into　the　theoretical　calculations　of　TiO2-based　commercial　photocatalysts　in　the　field　of　water　splitting　is　also　provided.　Finally,　the　calculation　of　TiO2-based　photocatalytic　water-splitting　simulations　is　summarized,　and　possible　future　research　and　development　directions　are　discussed.