Strong convection is characterized by the small spatial scale, short duration and sudden occurrence. Strong convective weather induces disasters and results in the losses of life and property. Chinese meteorologists have conducted a great deal of researches on the mechanism and characteristics of strong convective weather in northwest China. However, it is still difficult to forecast strong convective weather. It is necessary for meteorologists to continue their studies on strong convective weather. In this paper, we focus on a continuous 8-day rainy weather occurred in Shaanxi Province from May 8 to 15, 2009. A strong convective weather process occurred over the Loess Plateau of China on May 16th. Many studies reveal that there is often a low-level shear line or vortex before a strong convective weather occurs. However, this process does not occur under an obvious low-level shear line or vortex, but northerly winds. So it is difficult to forecast a severe short-duration convective weather. We tried to reveal the formation mechanism behind such events and provide the useful forecast ideas for future similar weather based on the NCEP analysis data, Weather Research Forecast (WRF)model forecasting data, observed data and Black Body Temperature (TBB)data by using common diagnostic analysis techniques. Results indicate that on May 16th there were two characteristics in the severe convective weather: Firstly, with upper-level low trough and the shear line o-ver the ground, a strong convective weather occurred after rainy weather for several days. Secondly, observed data shows that there was no shear line between northerly wind and southerly wind at 850 hPa and 700 hPa, there was a cyclonic curvature between northerly wind and northwesterly wind over north and central Shaanxi. Moreover, atmos-phere was relatively wet at 850 hP, and the near-surface atmosphere was stable. The upper-level low trough and the ground shear line afford a favorable weather situation for the development of meso-scale system. Strong convective in-stability and strong upward motion were conducive to the formation and maintenance of meso-scale convective cloud clusters. Synoptic scale systems of strong convective weather occurrence and precipitation were forecasted successfully by WRF model, so its forecasting data can be used to study the physical mechanism of the formation of strong convec-tion weather. Based on the WRF model forecasting data and per hour data from Automatic Weather Station in Shaanxi Province, thermal and dynamic conditions, such as moist static temperature, convective available potential energy, SI index, divergence, vertical wind shear and updraft, are analyzed. High-energy area of moist static temperature repre-sents the unstable, warm and humid air mass, but low-energy area represents the cold-dry air mass.