Abstract: Based on the dynamic effect of support while roof cutting during the periodic weighting in shallow seam min- ing,a system mechanical model composed by upper roof,immediate roof,powered support and waste rock was estab- lished in this study. The compression quantities of the support under dynamic loading after the system instability was obtained by using catastrophic theory and rock dynamics. The support dynamic loading effect was analyzed while roof cutting,and the working resistance of support was determined. The results showed that the support capacity was related to the cycle weighting interval,the upper load and the thickness of immediate roof,also related to the stiffness ratio of immediate roof and support and the material parameters when the system was unstable. The rotation and cutting of up- per roof and the unstable failure of immediate roof are main reasons for the support impact. The rationality of theoreti- cal derivation was verified by the coal mine.