Abstract: Aiming at the material composition and mechanical properties of the debris landslide, the theory that unload-load response ratio is taken as the evaluation parameter of landslide stability is put forward in the framework of system dynamics. Comparing and analyzing parameters of the unload-load response ratio and the load-unload response ratio, it is found that the unload-load response ratio parameters have more theoretical significance and practical application value in slope stability evaluation and engineering practice than the load-unload response ratio parameter. The unload-load response ratio parameter is determined and its feasibility is analyzed. Then, the model of unload-load response ratio, based on displacement acceleration and monthly rainfall, is established. As an example, the Xintan typical debris landslide is analyzed and calculated. The results show that the steady state reflected by the timing curve of the unload-load response ratio is consistent with the actual status. When Y' Y'- and Y'0,the overall unstability of landslide would appear. That shows it is available to use the unload-load response ratio to forecast landslide's deformation stage and as a criterion of landslide instability.