Abstract: The flow instability of supercritical water is an important aspect of thermal-hydraulic design of Supercritical Water-cooled Reactor (SCWR). The validated numerical simulation method helps to obtain the internal mechanism of flow instability, a wider instability boundary, and further deepen the understanding of supercritical water flow instability. Based on the experimental data of supercritical water instability that has been carried out, this paper carried out the verification of the calculation method; on this basis, using the system analysis program as a tool, the flow instability phenomena of supercritical water in parallel channels were systematically studied. In this paper, the inflection point of the influence of the supercritical water inlet temperature is obtained; the instable threshold power increase with the increase of the operating pressure at the same inlet temperature and the working fluid under the supercritical condition has better stability characteristics; the suitability of the dimensionless criterion is evaluated under supercritical conditions.