The invention discloses a preparation method of metal silver nanowires with adjustable length and diameter. The method comprises the following steps: dissolving silver nitrate in polyhydric alcohol for preparing solution; dissolving an alkali metal halide and a reducing compound in the polyhydric alcohol for preparing the solution; mixing the two types of the solution, and fully reacting under stirring to get the mixed solution; heating the polyhydric alcohol to 120-160 DEG C, dripping into the mixed solution, keeping the temperature and reacting for 15-44 hours; and performing centrifugal separation on reaction solution after the reaction, and washing lower-layer precipitate to get the silver nanowires. According to the preparation method, inert gas does not need to be introduced for protection, the reaction temperature is low, the preparation process is simple, the yield is high, the cost is low, and the insufficiencies of complex preparation procedure, low yield, high cost and the like in the template plate, the seeding method, the traditional polyhydroxy reduction method and the like can be overcome, thereby having important significance for large-batch industrial production and actual application thereof of the silver nanowires.