Tsunamis generated by submarine landslides have the potential to cause devastating consequences. A comprehensive understanding of the generation processes and characteristics of landslide-generated tsunamis is essential for improving tsunami hazard prediction and assessment. In this study, we investigated the generation and characteristic of landslide tsunami with numerical modelling constrained by geophysical interpretation in the Xisha Islands, South China Sea. The continuous landsliding processes significantly influence the initial characteristics of tsunami waves. The frequencies of landslide-generated tsunamis exhibit considerable variability due to the continuous landsliding deformation, which is also reflected in the variances of energy spectral density with frequencies. A continuous increase in energy spectral density with frequency leads to a delay in the maximum wave height; while a continuous decrease in energy spectral density with frequency results in longer waves, thereby reducing energy dissipation and producing greater wave heights during initial tsunami propagation in the tsunami generation stage. The wave time series reveals variable coherences at different frequencies in gauges exhibiting an increase/decrease in energy spectral density with frequency. Additionally, phase angle analyses indicate distinct lead/lag relationships that may affect the travel time of tsunami wave. This finding further indicates that tsunami warning system relying solely on a single propagation model to predict tsunamis might be less accurate when estimating both magnitude and arrival time for submarine landslide-generated tsunamis, potentially hindering effective evacuation efforts. This study substantially enhances our understanding on submarine landslide-generated tsunami and will contribute positively to hazard assessment and mitigation strategies.