Driven by the “Dual Carbon” strategic goals, county-level autonomous power networks have prominent strengths. They realize local consumption of high-proportion renewable energy, and support autonomous and controllable operation, which have become a critical pathway for county-level energy transformation and new-type power system construction in China. When the county-level autonomous power network operates in off-grid mode, grid-forming energy storage serves as the core unit for system voltage and frequency support. The virtual synchronous generator (VSG) and virtual impedance control strategies adopted by it will significantly alter its steady-state short-circuit output response. Superimposed with the heterogeneous short-circuit characteristics of multi-type renewable energy power sources (such as grid-following photovoltaic systems and small hydropower stations), the above characteristics pose a severe challenge to the accurate calculation of the system’s steady-state short-circuit current. To address this issue, this paper takes full account of the control characteristics of grid-forming energy storage and the differences in short-circuit output among multi-type power sources, establishes a steady-state short-circuit equivalent model for multi-type power sources including grid-forming energy storage, and proposes a Newton-Raphson method-based calculation method for steady-state short-circuit current of county-level autonomous power networks. The case analysis of a typical county-level autonomous power network and simulation verification via PSCAD/EMTDC show that the calculation error of the proposed method is less than 10%. The method can provide theoretical support for the type selection of electrical equipment and relay protection setting calculation of county-level autonomous power networks.