The invention provides a preparation method of probiotic fermented rice milk. Three probiotics of lactobacillus rhamnosus, lactobacillus paracasei subsp. paracasei, and lactobacillus brevis are used as original strains, and compound probiotic freeze-dried powder is obtained through amplification culture, powdery freeze-dried strain preparation, and freeze-dried powder complex formulation. The probiotic fermented rice milk is prepared by the following steps: obtaining rice, brown rice and drinking water according to a weight ratio of 2:1:7, performing pulp refining in a colloid mill, sieving by a 80-mesh fine sieve to prepare mixed rice milk pulp, adding 5% white sugar, performing liquefaction by high temperature resistant alpha-amylase, performing saccharification by glucoamylase, performing hydrolyzation by papain, inoculating the compound probiotic freeze-dried powder according to a ratio of 0.01%, allowing the powder to stand and performing fermentation for 4 hours, well mixing, and performing aseptic filling.