Herein, we reported a novel photoelectrochemical immunoassay method based on a target-triggered on/off signal of the ultra-structured Bi2O2S (BOS) photoanode system for the sensitive testing of carcinoembryonic antigens (CEAs) in serum samples. Well-defined three-dimensional sheet-like self-assembled flower-like Bi2O2S superstructures were obtained using a time-controlled hydrothermal method. Such well-shaped multifaceted surfaces were considered to be good laser cavity mirror surfaces for multifaceted reflection and refraction of excitation light in the material. An elegant enzyme biocatalytic strategy was introduced into the constructed detection model to sensitively detect CEAs. The substrate 4-chloro-1-naphthol (4-CN) was oxidized to 4-chloro-hexadienone (4-CD) under the formation of target-triggered immune complexes against mAb1 and peroxidase-modified mAb2. Subsequently, 4-CD produced by the biocatalytic precipitation reaction was transferred to the photoanodes of Bi2O2S nanoflowers (BOS NFs) to burst their photoelectric signals, thus achieving the quantification of CEAs. Through optimization of the conditions of the immunization protocol, a good negative photocurrent response to the target CEA was found in the wide range of 0.02-50 ng mL-1 with a detection limit of 11.2 pg mL-1. Impressively, the reported biocatalytic PEC sensing strategy on superstructures is comparable, or superior, to the gold standard ELISA kit in terms of sensitivity and the target response range. This study presents a target-mediated PEC immunoassay for biocatalytic precipitation based on a self-assembled superstructure of Bi2O2S, providing a fresh scheme for the analysis of disease-related markers.