The invention discloses a lithium sulfide series solid electrolyte material added with lithium tin alloy, silver iodide and silver chloride and a preparation method thereof. The preparation method comprises the following steps that (1) under the atmosphere protection condition, lithium sulfide, phosphorus sulfide, lithium tin alloy powder and sulfur are weighed according to a mole ratio of (2.5 to 4.0) to (0.5 to 1.0) to (0.02 to 0.1) to (0.01 to 0.05); the materials are uniformly mixed to obtain a lithium sulfur phosphorus and tin mixture; (2) under the conditions of atmosphere protection and safe red light, the lithium sulfur phosphorus and tin mixture, the silver iodide and the silver chloride are taken and are put into a ball milling tank to be subjected to ball milling; an amorphous state lithium sulfur phosphorus and tin mixture containing the silver iodide and the silver chloride is obtained; (3) the mixture obtained in the step (2) is sealed under the atmosphere protection condition; then, the temperature is raised to 100 to 200 DEG C under the vacuum condition; heat treatment is performed; the lithium sulfide series solid electrolyte material is obtained. The lithium ion conductivity of the obtained solid electrolyte material can be improved through simultaneously adding the lithium tin alloy, the silver iodide and the silver chloride.