A spoof surface plasmon polaritons (SSPPs) sensor based on liquid switch control is proposed to detect metal groove filling density. The sensor consists of liquid switch controllers and power division structure. The liquid switch consists of a plastic pipe and syringe with water, which is fixed on the branch structure of SSPPs sensor. By filling the plastic pipe with water, the branch cannot transmit signal, which is called “OFF” state. In contrast, when there is no water in the plastic tube, it is called “ON” state. By switching the “ON” or “OFF” state of sensor’s branches, it can control the sensing area of SSPPs sensor. The detection method is based on the change of reflection coefficient of SSPPs sensor caused by the change of groove filling quality. By switching the states of branches in turn, it can detect whether whether there are filling quality problems at each branch. The experimental results show that the SSPPs sensor can effectively detect the filling changes of 10 mg, which can be used for rapid detection of workpiece with mass production.