In the present experiment, by using the sounding rocket’s sub-orbital ballistic flight, realized the gravitational environment similar to that of liquid-fueled rockets during its coasting flight. In the low-gravity state, the cryogenic test fluid, liquid nitrogen, was introduced into the test sections which had similar shapes to the flow channels in the cryogenic propulsion systems. The boiling of liquid nitrogen inside the test-sections and the transition of flow regimes from gas/liquid two-phase flow to liquid mono-phase flow were successfully visualized. The temperatures, pressures and void fractions in each channel were measured as well. The mechanisms enhancing heat transfer were discussed based on the visualization. In the present case, compared with the corresponding ground test, it was confirmed that the two-phase flow in the complex channel could wet the heat transfer surfaces more easily due to the absence of gravity, and that more uniform chill-down effect could been obtained.