An effective atomization of liquid is of importance in the performance of combustion engines. For liquid hydrocarbon rocket engines with a staged combustion cycle for high-power application, the Gas-Centered Swirl Coaxial (GCSC) injector is widely employed. Gaseous oxidizer at high velocity enters directly through the center of the injector and is surrounded by a swirled liquid film injected along the periphery of the injection element. The swirled liquid film is stripped and fragmented into drops by the high velocity gas stream. The understanding of the atomization characteristics of the injector should be improved for the design of more reliable and efficient injectors dedicated to liquid rocket engines. In order to effectively evaluate atomization performances, it is essential to precisely predict liquid film dynamics inside the injector. The liquid film thickness and length are a function of the injector recess length, and they affect the atomized drop size. Internal flow visualization with a LIF (Laser Induced Fluorescence) method was conducted to investigate the overall form and the interface corrugation of the liquid flow at various swirl strength conditions. The swirl strength is varied by changing the inlet angle of tangential entry holes. The experimental results show clearly that the intact liquid length increases with increasing the swirl strength at the same dynamic pressure ratio. We also measured the frequency of the surface perturbations with a spectral method. We find that this frequency increases steadily with gas velocity, and appears to be independent of the initial swirl number.