A simple but powerful FLC （Fuzzy Logic Controller） design method in put forward by using sliding mode switching surface as a sole fuzzy input variable. It achieves good performance for liquid level control. The total number of rules of the single input fuzzy controller is greatly reduced compared to conventional FLC. The design and tuning of controllr are more simple and easy. At the same time this kind of fuzzy controller is equivalent to the quasi-sliding mode controller, so the robust property and stability is guaranteed well. Experiment result of a tank control shows that it is conscientiously feasible and deserves to be widely applied in the process of controlling industry.