Mixing flows of supercritical fluid and liquid assuming the supercritical hydrothermal synthesis(SCHS) reactor are calculated using the numerical method developed by our group. First, the influence of thermophysical properties near the critical point to the flows is evaluated. The flows ignoring density change and specific heat change become a steady-state flow and are obviously different from flows considering all thermophysical properties. These results indicate that the large density difference in fluid at a narrow region caused by a peak of specific heat induces unsteady flows in the reactor. While higher bulk pressure results in a steady flow because of the moderate change of thermophysical properties. Next the flows in a sub channel changing the width are calculated. The channel with a smaller width makes a strong injection and the mixing occurs mainly at the downstream of the main channel. The tiled sub-channel may suppress the flow recirculation in the main channel.