The invention discloses a method of identifying deviation of a welding joint of rotating electric arc gas shielded welding based on a rough set. The method utilizes a welding electric arc electric signal sensor, a welding electric arc position sensor, a data collecting card and the like to collect experimental data. Under a rough set modeling mode, the collected experimental data are used for constructing a decision table through a data preprocessing module, and a rough set model is constructed through an attribute reduction module, an attribute value reduction module and a rule reduction module. Under an online deviation prediction mode, the collected experiment data undergo processing by the data preprocessing module and are matched with the rough set model constructed under the rough set modeling mode. In addition, uncertain reasoning is utilized to predict deviation of the welding joint, and the deviation of the welding joint is output through a statistical module. According to the method of identifying deviation of the welding joint of rotating electric arc gas shielded welding based on the rough set, nonparametric modeling of identification of the deviation of the welding joint is achieved, system composition is simple, anti-interference capability is strong, engineering practicality is good, the welding joint deviation can be extracted in real time, and the method can be applied to a corresponding deviation device for real-time deviation.