After comparing the mechanism of tilted plume under stack effect with that of spill plume, the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of fullscale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel, and the range of flame deflection angle is about from 50 to 60 degree.