The S-doped g-C3N4 (SCN) was prepared by thermal condensation method using thiourea as a precursor, and then the phosphotungstic acid (PTA)/SCN composite photocatalytic material was prepared by reflux adsorption method. The photocatalytic degradation experiments of Rhodamine B showed that SCN20 had the highest photocatalytic degradation rate (74 %), which was 1.9 times and 3.5 times higher than that of PTA (39 %) and SCN (21 %), respectively. The photocatalytic degradation rate of SCN20 was increased by 5 times compared to that of SCN, indicating that the photocatalytic degradation performance of the composite material was significantly improved. The photocatalytic degradation mechanism study revealed that O2- was the main active species in the photocatalytic degradation of Rhodamine B, and the addition of PTA helped the effective separation of electrons-hole and improved the photocatalytic degradation rate. Our PTA/SCN is proposed as an environmental safety tool due to several advantages, such as low cost, convenient preparation, and efficient photocatalytic degradation of Rhodamine B.