In order to examine the forecasting error of the onset of Jianghuai Meiyu, 2010, the variation features of humidity, meridional wind, geostrophic westerly jet stream at the high and low levels and NCEP reanalysis data from June to July in 2010 as well as 21-year average conditions during 1985-2005 and variations in recent years were studied to confirm the regularity and universality of variation features about meteorological factors before and after Jianghuai Meiyu, providing new approaches and focus for Meiyu forecasting in Jianghuai. The study found that during some years the jump of westerly jets from 30°N to 30-37.5°N is a significant starting signal of Meiyu in Jianghuai, and its stable maintenance helps sustain the rainfall of in Meiyu season. The time interval and persisting period for northward jump of 70% humidity region to 30°N are effective indexes for forecasting Meiyu onset and its length. In 30-35°N region, the sudden increase of wind differences (v_{850 hPa}-v_{200 hPa}) may correlate with the Meiyu onset in Jianghuai. These findings offer new ideas for Meiyu forecasting in Jianghuai.