Abstract: Affected by the Northeast China Cold Vortex, two squall lines successively entered the Bohai Sea from the west coast on the night of 12 June 2022. The first squall line weakened rapidly after entering the sea, and the second squall line maintained its intensity and strengthened slightly. This study used ground automatic station observations, Doppler weather radar data, Tianjin Meteorological Tower data, ERA5 reanalysis data, RMAPS-NOW system analysis data, and other multisource data to compare and identify the possible causes of the different intensity changes of the two squall lines after entering the sea. The results indicate that the intensity difference between the two squall lines after entering the sea is a combined result of multiple factors. The stronger the storm structure of the squall line before entering the sea, the smaller the distance from the main body of the squall line to the gust front, which is more conducive to the maintenance of the squall line after entering the sea. The moist tongue extending from the ocean to the inland, the transition to the converging flow field on the front side, and the sustained strong environmental vertical wind shear, along with CAPE (convective available potential energy), provide favorable mesoscale environmental conditions for the second squall line to maintain its intensity. The ascending motions formed by the inflows on the front sides of the two squall lines and the outflows from the cold pools on their rear sides closely adhere to the main bodies of the lines, which is conducive to the continuous transportation of warm, moist airflow to the edges of the main bodies and subsequent lifting, allowing the CAPE to be fully released and promoting the vigorous upward development of the storm structures. In addition, the interactions between the intensities (propagation speeds) of the cold pools of the two squall lines and the lower-level environmental vertical wind shear as the lines enter the sea are identified as one of the important reasons for the differing intensity changes of the squall lines after entering the sea. An approximately equally enhanced cold pool intensity and an equally increased environmental vertical wind shear are conducive to the maintenance of squall lines.