Previous study of our group showed that two dense granular impinging jets would give rise to a liquid-like granular sheet (Shi et al., 2018). In current work, the dynamic characteristics of the granular sheet are studied using a high-speed camera, and it is found that the granular sheet undergoes an asymmetric oscillation at low jet velocities and high solid fractions. Effects of the granular jet velocity, the solid fraction, the impinging angle, and the particle diameter on the granular sheet oscillation and particle dispersion are investigated. Results show that time-averaged oscillation frequencies of granular sheets increase linearly with the granular jet velocity, but are nearly not affected by the impinging angle. Time-averaged oscillation amplitudes of granular sheets increase with the propagation distance, granular jet velocity and impinging angle. The vertical and stable granular sheet evolves to an asymmetric oscillation as the disturbance of the granular jet increases, which causes the momentum imbalance of the impinging jets at the impact point, and consequently results in the asymmetric oscillation of the granular sheet.