Abstract: Geothermal energy, as a clean, stable, and renewable resource, plays a critical role in facilitating clean heating in northern China and promoting the national energy transition. Nevertheless, the field currently lacks dedicated numerical simulation software tailored specifically to geothermal applications. General-purpose simulators developed for petroleum engineering, hydrogeology, or thermal engineering are widely used in geothermal simulations, yet they often fail to adequately address the unique requirements of geothermal resource development. Furthermore, existing simulation tools are frequently characterized by complex user interfaces and steep learning curves, posing significant barriers for novice users. In response to these challenges, this study developed a specialized software—GeothermalKits—designed exclusively for geothermal development and utilization. Building upon an integrated open-source numerical simulation core, the software incorporates our proposed optimization algorithms for geothermal reservoir engineering and provides a suite of professional modules essential for the geothermal industry, including well spacing optimization, resource assessment, coaxial casing heat exchange simulation, U-shaped well heat exchange simulation, and carbon emission reduction evaluation. These modules cover various scenarios in geothermal development, including shallow and deep geothermal systems, heat exchanger systems, hydrothermal systems, seepage effect, heat transfer, and power generation. The accuracy of GeothermalKits has been verified by comparing its results with field data or analytical solutions. In addition, a user-friendly interactive interface and streamlined operational processes, such as “one-click execution”,significantly lower the entry barrier, enabling practitioners from diverse disciplinary backgrounds to rapidly attain proficiency. This development not only facilitates the broader adoption of numerical simulation technologies within the geothermal sector but also offers robust technical support for the scientific evaluation and sustainable management of geothermal resources.