The invention relates to a preparation method of sodalite-red phosphorus synergistic flame retardant. The preparation method includes: mixing the sodalite with a certain amount of 0.1mol/L of a NiCl2 solution prior to filtering, cleaning, washing and placing in a quartz tube reactor after ion exchange under the temperature of 60DEG C for 30-150 minutes; feeding hydrogen under the temperature ranging from 400DEG C to 450DEG C for 20-90 minutes prior to feeding hydrogen phosphide under the temperature ranging from 410DEG C to 440DEG C for 2-10 minutes, and finally heating and warming the sample in an air-insulated reaction vessel under the temperature ranging from 260DEG C to 290DEG C for 10-60 minutes to obtain the sodalite-red phosphorus synergistic flame retardant loading 4%-30% of the red phosphorus by mass ratio in pore passages. The preparation method is simple in process, the shortcoming existing in independent use of the red phosphorus flame retardant is overcome, and the flame retardant is good in flame retardant performance.