By using conventional data, as well as AWS(automatic weather stations) and NCEP1°× 1° and FY2E T_BB data, the causes of regional rainstorm in Shandong from July 31 to August 1 2012 are analyzed.The results indicate:(1)The low-level shear line and cold front were a major weather system of the rainstorm. The high-temperature and high humidity and strong southeast flow provided temperature and humidity conditions in the rainstorm area. (2)Low-level frontogenesis forced ageostrophic vertical circulation into effect. When the updraft was strengthened, precipitation intensity increased. The frontal zone and the southerly winds in 925 hPa which moved between north and south in the rainstorm area made the unstable energy released and rebuilt. (3)The moist baroclinic items of the moist potential vorticity was negative value in 925 hPa during rainstorm,which should be attributed to the low-level baroclinic enhancement of frontogenesis. The area and intensity of rainstorm increased when the baroclinic items enhanced. (4) When the convective cells generated and strengthened,the precipitation area and intensity increased. T_BB center located in the right of the low-level shear line and the frontal surface, but the heavy precipitation center located in the area superimposed by the T_BB center and the low-level weather systems.(5) The area of the cyclonic crook in the left of the ground convergence line which was consistent with the large value area of contour behind the T_BB center was the heavy precipitation.(6) The mesoscale dryline and surface convergence line was the rainstorm mesoscale systems. The dryline which was significant for the area of rainstorm was always behind the convergence line.