Abstract: This study aims to find out the causes for the dissolution of unqualified samples found during evaluation sampling of lansoprazole enteric-coated preparations by the laser infrared imaging system and orbitrap high resolution mass spectrometry, with suggestions for improvement. Lansoprazole enteric-coated preparations were tested by current standard, the dissolution of a batch of samples was below the limit and other items were in line with the standard. Considering that this product is unstable to acid and alkali, the following exploratory experiments were designed from different dimensions, based on the conclusion of the unannounced inspection of the company, to explore the reasons for the unqualified batch, including the influence of high-temperature and high-humidity storage environment on the key quality properties of the sample, the influence of 2-hour acid resistance test on dissolution result, the imaging of the core and the measure of coating layer thickness, the optimization of chromatographic conditions of related substances, and the analysis of the source of impurities. It was found that improper storage in circulation and poor coating process caused the low dissolution of this batch: the high-temperature and high-humidity storage environment possible in the circulation process led to the decreasing efficacy of disintegrating agent in the samples and thus the difficulty to release the active pharmaceutical ingredient fully; the coating solution could not be uniformly sprayed on the core, resulting in thin isolation layer and different thickness, which then affected the protection of the main drug against acid degradation. The above two reasons together resulted in unqualified dissolution of this batch. The overall quality of lansoprazole enteric-soluble preparation is good, but the formulation and process in some companies need to be optimized; and the temperature and humidity in the circulation process need to be controlled in strict accordance with the regulations.