Dopamine (DA) is an important neurotransmitter. Abnormal levels of it in human body can increase the risk of many neurological diseases. Thus, developing a simple, sensitive detection method of DA is crucial. In this paper, we reported a "signal-off" anodic PEC sensor based on fluorine-doped tin oxide (FTO) glass modified ZnInS/TiO heterojunction (ZnInS/TiO/FTO) for DA detection. The experimental results show that the ZnInS/TiO/FTO electrode prepared by two-step hydrothermal method has a good photocurrent response performance under visible light. After incubation with DA, the photocurrent response decreases significantly because DA can rapidly oxidizes to polydopamine (PDA) through the action of superoxide radical (·O) and hydroxyl radical (·OH) intermediate species, which are intermediates produced by the ZnInS/TiO/FTO electrode under visible light irradiation. The constructed PEC sensor has a good linear relationship in the concentration range from 0.5 to 1000.0 μM, and its detection limit is 0.253 μM. In addition, the results of the proposed PEC sensor in real serum samples are satisfactory. The PEC sensor provides a promising platform for DA detection, laying the foundation for future advances in disease diagnosis and prevention.