Self-oscillating gel is a class of deformable polymers driven by Belousov-Zhabotinsky (BZ) reactions, which can form periodic deformations without any external stimuli, and are widely used in the research of biomimetic creeping robots. However, quantitative analysis on the self-oscillating gel from perspective of energy conservation is still limited. This work adopts frequency domain analysis to the chemo-mechanical model, and the basic frequency is obtained to evaluate the maintenance energy of the BZ gel. For accurate computation, boundary value problem with unknown period is formulated. Then, continuation algorithm based on perturbation technique is performed to obtain the oscillating trajectories for varying model parameters. The results could be implemented to design self-oscillating gels with prescribed periodicity.