The invention provides a quaternary phosphonium sulfonate fire retardant and a synthesis method and use thereof. The structural general formula of the fire retardant is as shown in a formula (I) in the specification, wherein R1 and R2 are one of C1-C24 alkyl, C2-C24 alkenyl, C3-C24 cycloalkyl, C4-C24 aryl, and C4-C24 substituted aromatic of which the substituent group contains N, O or P. The fire retardant is prepared from sulfonyl chloride, alcohol, an organic phosphorus compound and the like as raw materials by reaction in two steps. The synthesis condition is mild, operation is simple and convenient, and yield is high. Meanwhile, the fire retardant has good heat stability, and has good flame retardant efficiency when being applied to a plurality of polymers, UL-94 of the obtained PC fire-retardant composite material achieves the V-0 grade, UL-94 of the obtained POE fire-retardant composite material achieves V-2 grade, and meanwhile, good chemical and thermal properties are kept.