In August, it is an unfrequent event that there is a storm surge with a height of 518 cm caused by the effects of extratropical cyclone at the Bohai Sea. Using the weather charts, satellite cloud pictures, observations from automatic weather stations and the surge data from the Tianjin Oceanic Administration, the characteristics of two abnormal increasing water events by the storm surges occurring on Tianjin Harbour in August 2008 were analyzed. The influences of meteorological factors on storm surges were summarized. They can offer valuable information for predicting storm surges. The paper discussed the occurring conditions of storm surge and increasing water on account of the offshore wind (northwest wind). The results show that the extratropical storm surge has the characteristics of highintensity for increasing water (the largest height is 121 cm) and long duration time (for 15 hours). The paper also proposed the differences between the water increased by cyclone and by typhoon. And the reasons for occurring storm surges in a semiclosed and shallow gulf were analyzed based on the propagating theory of Kelvin wave.