The climate system is nonlinear and non stationary, in addition, it is also hierarchic, thus it is a multi level structure formed by many different spatio temporal scales, and each spatio temporal scale has different predictability and stability respectively. When we research a meteorological drought index, we generally consider the precipitation, temperature, relative moisture of soil and other essential factors in certain period of time. By taking account of the climatic characteristics of different regions, the comentropy method is first used to obtain the two intrinsic scales of zonal precipitation i.e. the homogeneous state intrinsic scale and the variational state intrinsic scale because of the conception that the climate system is nonlinear, non stationary and hierarchic, then a new meteorological drought index named MSPI is developed. Afterwards, the appearance, development, continuance and alleviation of the severe meteorological drought in the middle and lower reaches of the Changjiang River in 2011 are taken as an example to examine the ability of MSPI to monitor the meteorological drought. The result shows that MSPI can monitor meteorological drought at different grades and can distinguish the course of meteorological drought perfectly. Taking all factors into consideration, we think that the MSPI is an efficacious meteorological drought index which can meet the demands to monitor and detect meteorological drought. In practice, the MSPI could be as a useful complement to other meteorological drought indices.