The present invention relates to an active power steady-state security region construction method considering single TCSC (thyristor-controlled series compensation) equivalent reactance parameters. According to the method, thyristor-controlled series compensation equivalent reactance parameters and node active power are combined creatively; according to a problem that an existing active power steady-state security region construction method does not consider TCSC equivalent parameters, a method of correcting the injection power of nodes is adopted to replace a method of changing the structuralparameters of a power grid to influence the distribution of power flow, so as to analyze TCSC; the display expression of an injection power space active power steady-state security region consideringsingle TCSC equivalent reactance parameters is theoretically inferred; and a problem that a traditional method needs to traverse TCSC equivalent reactance values and generate a series of active powersteady-state security regions one by one can be solved. Combined with engineering practices, the method of the invention has high analysis efficiency and can satisfy on-line steady-state security assessment.