In this study, ferrous oxalate (FeC2O4) used as an effective heterogeneous Fenton catalyst, was inexpensively synthesized by a chemical precipitation method. The attractive efficiency was investigated to demonstrate the underlying mechanism of in-situ reactivation. Based on the mechanism, the important issue of effective performance suggested that the reactivation of active sites enhanced the activation of hydroxyl radical((OH)-O-center dot) for degradation. In addition, the catalytic performance for industrial application was studied by evaluating the degradation of methylene blue (MB). In the typical process, a degradation efficiency over 94% was observed at 10 min, and it was improved to over 95% at 3 min under irradiation with a xenon lamp. The catalyst has high operational stability and reusability properties in the process. Remarkably, self-activation of the catalyst was observed during the recycling processes.