For investigation of the feasibility of cofiring high sodium coals (HSC) mixed with coal gangues (CG) to inhibit fouling and slagging of coal ash，thermogravimetric analyzer and fixed bed reactor were used to evaluate the cofiring performance and effect on Na fixation in coal ash. By comparison of Na content in ash before and after combustion，the effect of cofiring on Na fixation was evaluated. By comparing the differences of weight loss and mass change rate between theoretical and experimental combustion，the synergistic of cofiring was confirmed. The results show that the Na forms in HSC mainly consist of H2O-soluble，HCl-souble and NH4Ac-soluble Na，while the Na-containing compounds cannot be detected with XRD analysis before and after combustion. Cofiring effectively enhances the residual of Na-containing compounds in ash，the Na retention in ash increases by 50%-75% through cofiring 10% CG with 90% HSC，thus verifying the effectiveness of Na fixation in ash. Meanwhile，cofiring enhances the combustion rate and reduces the peak temperatures of the mixed fuel，and shows obvious synergistic effect. By further optimizing cofiring conditions，it is expected to realize synergistic，efficient and safe conversion of HSC and CG，which favors the energy conservation and emission reduction undoutedly.