Abstract: In order to improve the reliability of transformer longitudinal differential protection, a fuzzy adaptive longitudinal differential protection of transformer is proposed in the paper. When a fault occurs in the protection zone, the fuzzy logic can reduce the resistance coefficient automatically. It results to increase the sensitivity of protection. Besides, when a fault happens out of the protection zone, the fuzzy logic can adaptive increase the resistance coefficient. It enhances the reliability of protection. Finally, the Simulink simulation is done on Matlab. It is result that the proposed fuzzy adaptive longitudinal differential protection of transformer is better than the longitudinal differential protection of transformer.