Abstract：Perilous rock formation is the result of multiple correlated factors coupling. It is found that the inside factors of perilous rock are geomorphology，geologic structure and rock layer，etc.，and the outside factors are rainstorm，earthquake，ground water，weathering，vegetation and unreasonable mankind engineering . Based on the norm theory，the influence factors of perilous rock are measured by analyzing its influence factors and adding to the two norm numbers near and far distances. The correlation and weight coefficients of factors are obtained. Taking Wanzhou Taibaiyan perilous rock，in the area of Three Gorges Reservoir，as an example，the grey correlation of the norm of Taibaiyan perilous rock is calculated. The result shows that the first controlling factors of perilous rock is the main controlling fissure，and the second factor is groundwater，which affects formation and stability of perilous rock foundation，and dip angle of free face，height and weathering perilous rock. The results can provide significant reference to the acknowledge of the disaster of perilous rock in the Three Gorges Reservoir.
