The invention relates to the technical field of a lithium ion battery and particularly to an inorganic solid-state electrolyte material and a preparation method therefor. Reaction raw materials are weighed based on a molar ratio of Li<+>:Al<3+>:M<4+>:P<5+> being equal to (1+x):x:(2-x):3; the reaction raw materials are mixed with deionized water to obtain a mixture; the mixture is heated and stirred, and moisture is evaporated to obtain a viscous material; the viscous material is sintered at a low temperature, and then is subjected to high energy ball milling to obtain an Li<1+x>AlM<2-x>(PO4)3 (x is greater than or equal to 0 and less than or equal to 1) electrolyte powder, wherein M is Ti, Ge, Zr, Hf or Sn. The inorganic solid-state electrolyte material and the preparation method therefor are characterized in that the electrolyte material is simple in preparation process, relatively low in sintering temperature, and relatively high in conductivity (10<-3>Scm<-1>), and the obtained electrolyte material can be used for an all-solid-state lithium ion battery.