<p>As sudden-onset geological disasters, the dynamic behavior of rock avalanches is significantly influenced by the size of the debris particles formed during rock mass disintegration. In this study, 59 sets of laboratory model tests were conducted to systematically investigate the effects of particle size on the characteristic parameters of landquake signals (Arias intensity, mean of the envelope, mean frequency, and vibration energy), and to explore the roles of release height and particle mixing. The results indicate that as particle size increases, the intensity-related parameters (Arias intensity, mean of the envelope, and vibration energy) exhibit exponential growth, while the mean frequency decreases exponentially. This suggests that larger particles release higher energy at lower frequencies—a particle size effect that is independent of release height and thus of universal validity. Granular flows with mixed particle sizes display an inverse grading characteristic during movement, causing the landquake signal characteristics to be biased toward those of the finer particles. This confirms that the landquake signal is primarily generated by the interaction between the lowermost layer of particles and the base plate. These findings provide a theoretical foundation for inverting rock avalanche particle size characteristics from landquake signals and for disaster early warning.</p>