Abstract：According to longitudinal balance of own weight of chimney，the compressive region by sudden load of its own weight on cutting-support after blasting is analyzed；and the damage of the support from sudden load can be estimated by kλ≥0.85，which is height coefficient of the compressive region. While the chimney breaks down，brittle failure will be seen in the support position with large eccentric pressure；and plastic joint is formed. According to the nominal ensure coefficient k≥1.5，it can be judged that the chimney falls in. The limit position of backward moving neutral axis is determined by longitudinal balance of chimney weight and moment formed by loads in tensile region and resistance force on compressive region. If the limit position of the neutral axis is in the canister，the plastic joint of the support will remain when the chimney tilts slightly. At the time the damage of front shear region of support determines the dipping direction of chimney. When the angle of direction window is not greater than 30°and height of cutting is less than 2.4 m，the error of dipping direction will not be more than 2°. The initial dipping backward sitting is estimated by sloping coefficient Ks of backward shear of support. It is demonstrated by practical examples and estimation that backward shear is able to take place above the cutting on high chimney，which is higher than 50 m. In order to ensure the chimney not to tilt in longitudinal direction，the radius angle of the cutting is 210°–230°. To prevent the cutting on high site from backward shear，lower cutting should be blasted after 1.5–4.0 seconds when the cutting blasts.
