In order to study completely the atomization characteristics of mixing cavity of the designed new type tripropellant injectors, model injectors are designed for experiments under multiple operating conditions. Through experiments it can be seen that different curves of regularity for variations of SMD along with pressure drop of gas as well as mass ratio of gas to liquid ALR will be gain if the pressure drop of liquid remains constant while transform the pressure drop of gas. So do the other case only transforming the pressure drop of liquid. Moreover, these curves show the regularities. A great deal of experiments indicate the curves of average diameters SMD along with mass ration of gas to liquid ALR have the same trends although obvious differences exist between curves that SMD along with pressure drop.