Phosphorus is a key nutrient element limiting grassland ecosystem productivity. It is of great significance to clarify soil phosphorus distribution and its influencing factors for maintaining sustainable development of grassland ecosystem on the Qinghai-Tibet Plateau. In this study, we collected soil samples from different grassland types (i.e. meadow steppe, typical steppe, and desert steppe) along the horizontal transect of the Qinghai-Tibet Plateau from northwest to southeast. The distribution characteristics and influencing factors of soil total phosphorus, available phosphorus, and inorganic phosphorus and organic phosphorus fractions were investigated. The results showed that the total and available phosphorus contents in soil were the highest in meadow steppe, followed by desert steppe and typical steppe. The inorganic phosphorus fraction of all grassland types was dominated by acid-soluble inorganic phosphorus; the organic phosphorus fraction of meadow steppe soil was dominated by sodium hydroxide organic phosphorus, while acid-soluble organic phosphorus fraction was dominated in typical and desert steppe soils. Among different grassland types, the contents of water-soluble, sodium bicarbonate, sodium hydroxide inorganic phosphorus and various forms of organic phosphorus in the meadow steppe soil were significantly higher than those in the typical and desert steppes, while the content of acid-soluble inorganic phosphorus in the desert steppe soil was significantly higher than that in the typical and meadow steppes. Redundancy analysis showed that soil organic carbon, average annual rainfall were the main factors affecting the total and available phosphorus, average annual rainfall and free iron oxide were the main factors affecting inorganic phosphorus fractions, while pH, average annual temperature, above-ground biomass and average annual rainfall were the main factors affecting the organic phosphorus fractions. Structural equation model indicated that grassland type had a direct effect on both inorganic and organic phosphorus fractions, and annual average temperature and bulk density also had a direct effect on inorganic phosphorus fractions, while altitude, annual rainfall and annual average temperature had indirect effects on inorganic and organic phosphorus fractions through grassland types. The results of this study are of great significance for the effective management of soil phosphorus nutrient and the sustainable utilization of grassland resources on the Qinghai-Tibet Plateau.