The invention discloses a preparation method of low-cost polyphenylene sulfide, and relates to the field of macromolecular materials. The preparation method is characterized by using sodium sulfide and paradichlorobenzene as raw materials, using sodium benzoate and caprolactone as catalysts, using N-methyl pyrrolidone as a solvent, and using sodium hydroxide as an additive, and a specific technological process in production sequentially comprises the following steps: feeding the sodium sulfide, feeding the paradichlorobenzene, dissolving the catalysts, pre-polymerizing, polymerizing again, filtering, washing, drying, and packaging, so as to obtain a polyphenylene sulfide product. The preparation method has the advantages that a lithium chloride catalyst in the existing domestic main technology is not used, and the low-cost sodium benzoate and caprolactone are used as the catalysts, so that the production cost is reduced; all raw materials are dripped by several times at normal temperature, so that the polymerization reaction is performed within a certain temperature range, so as to effectively prevent heat releasing implosion during the polymerization reaction, improve the polymerization degree and various mechanical properties of the polyphenylene sulfide, and thoroughly solve the problems of instability, low molecular weight and poor property in the traditional technology product.