The test of slagging on water cooled wall was performed in a lab-scale entrained-flow gasifier. The gasifier’s slag surface morphology at different temperatures was studied and analyzed quantitatively. The equivalent temperature (T) was proposed

which was the ratio of slag real temperature and ash fusion temperature. The slag surface roughness was obtained by using ImageJ image analysis software. The slag surface was smoother when T>1. 0 than that of T<1. 0. Using fractal theory

the geometric characteristics of slag surface were quantitatively shown by fractal dimensions

and the relationship between equivalent temperature and fractal dimensions was found. The results showed that the whole spread of molten slag particles required T be greater than 1. 0 too.