Abstract: The supercritical water-cooled reactor (SCWR) is one of the six reactor technologies selected for research and development under the Generation-Ⅳ program. SCWRs are extensively attractive because of the significant economical competitiveness. In present study, a code TACOS (transient analysis code of SCWR) was developed to analyze the safety characteristics of SCWR with mixed spectrum core (SCWR-M). The steady state calculation of SCWR-M was carried out with TACOS. The results of steady state agreed well with the design value. Preliminary analysis of partial loss of flow accident was performed. The results indicate that the maximum cladding surface temperature (MCST) during the accident is 702.6 ℃, which is obviously lower than the limiting value of MCST. During the accident of partial loss of flow, reactor core can recover to safe state without additional action.