Abstract: Cold flow spray tests utilizing water and air to imitate gas and liquid oxygen in subcritical conditions and firing tests using liquid oxygen and gas in supercritical pressure for coaxial injectors have been done.Cold spray characteristics are investigated,such as flow rate,atomization and mixing,influences of gas and liquid on these characteristics,and combustion performance of coaxial injectors at supercritical pressures are completed.The strong and weak points of four coaxial injectors are obtained from these cold and firing tests.