Abstract: The classical Culmann's way still has vitality and application worth to the critical height problem of slope on engineering geology and geotechnical engineering. The Culmann's formulas calculating critical height of ordinary, vertical and fissure slopes are induced, the application ways and conditions of the formulas are refered. The engineering application of the formulas are demonstrated with a landslide engineering,a cutting slope,a pit of retaining wall and a natural dangerous rock slope.