Abstract：The fast weathering universally takes place in red bed mudstone slope，which is not completely solved till now. By selecting the typical red bed mudstone slope and monitoring its fast weathering in the field，it is shown that the fast weathering of the red bed mudstone slope is from surface to inside and mainly appears within 10 cm in depth below the surface，and that the variation of air temperature and rainfall has important affects on the fast weathering of the red bed mudstone slope. According to the mudstone block weathering experiments，it is also confirmed that the block weathering is very slow in the condition of unchangeable daily air temperature and moisture content. Based on the mudstone block temperature variation experiments and the finite element analysis，it is concluded that the main external factor affecting the red bed slope fast weathering is the rainfall in the high temperature state；and it offers a theoretical foundation for the ecological protection of the red bed mudstone slope.
