Aimed at the limitation of conventional Ziegler-Nichols parameter tuning method widely used in PID controller design,based on the geometric characteristics of system step-response curve,this paper gets three parameters of PID controller changing with circumstances under the condition that overshoot is strictly limited by calculating the area enveloped by the step response curve.The new tuning method can keep the little overshoot for the system and ensure a fast response speed,which makes up for the deficiencies of traditional PID parameter tuning method to some extent.This tuning method is applied to the boiler steam pressure control system design,and the simulation results shows that the new tuning method has a better transient performance compared with the classical Ziegler-Nichols method.