Abstract: Using the composite radar reflectivity data, the operational observation data and the NCEP daily reanalysis data, the environmental characteristic of the line MCSs that occurred in the middle and lower reaches of the Yangtze River in June and July 2010 is compositely analysed. The results show that the middle and upper tropospheric storm-relative flow field is of primary importance in determining the organizational mode of the linear mesoscale convection. The trailing stratiform MCS and the training line adjoining the stratiform MCS show front to rear storm relative winds in the troposphere, while the leading stratiform MCS shows lower tropospheric front to rear storm relative winds and upper-tropospheric rear to front storm relative winds.The low and mid level wind shears are largely parallel to convection line for the training line adjoining the stratiform MCS but perpendicular to convection line for the trailing stratiform MCS as well as the leading stratiform MCS.The parallel stratiform MCS and the quasi stationary back built MCS experienced significant middle and upper tropospheric line parallel storm relative winds with the increasing magnitude with the increasing height. The training line adjoining the stratiform MCS on 8 July formed on the cool/north side of a cold front and in unstable air conditions. The quasi-stationary back built MCS on 7 June formed in a changing high moisture and highθe surface environment. The most favorite environment for producing and developing the linear MCSs is that of high temperature and high humidity.