The present invention relates to a galvanized sheet detecting method in depth belonging to the field of galvanized sheet detection, which comprises steps below: a. Peeling off passivating coating of a galvanized sheet; b. Detecting foreign matter content of the passivating coating; c. Peeling off a galvanized coating; d. Detecting foreign matter content of the galvanized coating. The galvanized sheet detecting method in depth of the present invention can peel off the passivating coating from the galvanized coating and galvanized coating from a steel base coating in sequence to clear up reactions, ensure volatile elements Hg and Pb are completely transferred to solutions without loss, authentically, effectively and accurately detect portions of hazardous substances in each layer, adapt to demands for galvanized sheet production quality control and detection and bring a broad industrial application prospect.