Abstract: Steady-state security region（SR） is a powerful tool for assessing and controlling the steady-state security in bulk power systems with high penetration of intermittent and stochastic renewable energy, while tracking the security region boundary（SRB） is a bottleneck for SR application. To bridge the gap between the SR application and SRB tracking, this paper developed a general approach to approximate the SRB. A set of SRB points with different power stress directions were tracked by a developed general optimization model whose objective function is to maximize the steady-state security margin with satisfaction of specific secure constraints. For the explored set of SRB points, a piecewise approach was further developed to approximate the SRB with the explored SRB points by using hyperplane, and the SR in 2-and 3-dimensional active power injections space are then formed. The WECC-9 bus test case and the Polish 2736 bus test case are all used to evaluate the performance of the proposed approach, the results confirm that the proposed approach can realize to approximate the SRB precisely and form accurate SR in power system security situational awareness and control.