Using the conventional observations, satellite images and, Doppler radar and NCEP, 1°×1° reanalysis data, a comparative analysis is made of the MCS (Mesoscale Convective System) developing characteristics, environmental conditions, and triggering mechanisms between the two regional rainstorms on 30 July 2012 and 9 July 2013 in Shandong. The results show that the two processes were caused by the shear lines at 850 hPa; the lineshaped MCS was the direct cause, and the ground convergence line triggered the rainstorms. They have different synoptic systems at 500 hPa. The rainstorm on 30 July 2012 occurred under the domination of highlevel stepped slot, but the rainstorm on 9 July 2013 occurred in a typical context of “high in the east and low in the west.” The water vapor supply of the rainstorm on 30 July 2012 was from the East Sea and Western Pacific Ocean, and dynamic conditions were more favorable, with the water vapor flux divergence and specific humidity at 925 hPa being 10 g〖DK〗·hPa-1〖DK〗·cm-2〖DK〗·s-1and -0.2 Pa〖DK〗·s-1larger than those on 9 July 2013; while the storm on 9 July 2013 carried water vapor to the raining area from the South Sea, whose moisture conditions were more favorable. For two processes, the occurrence and development processes of MCSs and the ways to form and the structure at the mature stage were significantly different. In the rainstorm process on 30 July 2012, convective cells gradually merged into βmesoscale and finally into αmesoscale convective systems. In the storm on 9 July 2013, multiple convective cells merged into βmesoscale. Analyzing their trigger mechanisms, it is found that key points of shearline rainstorm trigger mechanisms are the formation and strengthening of the ground convergence line,as well as the frontogenesis caused by cold air intrusion.