The mean amount of summer precipitation in Shandong in 2017 was 453.0 mm, 13.2% more than the normal value (400.3 mm). The precipitation events were more and the spatial distribution was uneven. The polar vortex in the summer of northern hemisphere was characterized by monopole type distribution. Zonal circulation prevailed in middle and high latitudes. The intensity of western Pacific subtropical high was higher compared with the same period of normal years and the westextending ridge was to the west of that in normal years. The precipitation in June was mainly caused by stronger cold vortex in North China and Northeast China, while the more precipitation in July and August resulted from stronger and westward subtropical high and abundant water vapour in the warm and wet air current near it. The importance of similar years and objective prediction method were further analyzed.