The invention discloses an interval compression-based system impedance calculation method. The method is characterized in that equivalent system impedance of a substation bus on one side of a circuit is regarded as a function on equivalent system impedance of a substation bus on the other side, so that a solving process of a nonlinear equation set is converted into a problem of obtaining an intersection point of two hyperbolas; an intersection point of right branches of the two hyperbolas is a feasible solution of the to-be-solved nonlinear equation set; and a possibly existent interval of the intersection points of the hyperbolas is gradually compressed through an iterative process, and when the length of the interval can meet a calculation precision requirement, one point is taken as the feasible solution in the interval. According to the method, the convergence of the iterative process during solving of the nonlinear equation set is ensured; an error range after each iteration can be easily estimated; the deficiencies of relatively high requirements on a power network simulation model and relatively complex implementation process of a program simulation method, difficult initial value selection and multi-iterative attempts of an existing numerical solving method and the like are overcome; and engineering application is better facilitated.