Propagation characteristics of continuous rotating detonation wave near the operating boundary are presented. A series of tests have been carried out, and an operating domain is obtained, beyond which the continuous rotating detonation wave cannot be maintained. Based on the high frequency pressure measurements, flow-field structure in a continuous rotating detonation engine (CRDE) is constructed. The features include an upstream detonation wave and a downstream oblique shock wave. Propagation velocity deficits of the detonation wave have been calculated, and a critical value of 15-16.5% is obtained. When the velocity deficit is less than the critical value, the reactants are mainly consumed by the upstream detonation wave. Otherwise, further heat release may occur when the unburned mixture encounters the downstream shock wave.