This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faults of the Chinese mainland, that is that on an individual fault portion earthquake(s rupture-scale varies cycle to cycle, and hence earthquake(s strength changes with time. The tendency of this variation has no necessity. On defining relative size of rupture scales, a statistical result shows that it is of the lowest probability that ruptures with the same scale occur in two successive cycles. While the rupture(s scale in the preceding cycle is (small(, the probability of the following rupture(s scale being (large( is as many as 0.48. While the rupture(s scale in the preceding cycle is (middle(, the probability of the succeeding rupture being (small( or (large( scale is 0.69 or 0.25. While the rupture(s scale in the preceding cycle is (large(, the probability must be zero for the following rupture with (large( scale, and is 0.36 or 0.64 for the following rupture with (small( or (middle( scale. The author introduces and improves the cascade-rupturing model, and uses it to describe the variability and complexity of rupture scale on individual fault portions. Basic features of some active strike-slip faults on which cascade ruptures have occurred are summarized. Basing on these features the author proposes principles of cascade-rupture segmentation for this type of faults. As an example to application, the author segments one portion of the Anninghe fault zone, western Sichuan, for its future cascade rupture, and further assesses the probable strength and its corresponding probability of the coming earthquake. This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faults of the Chinese mainland, that is that on an individual fault portion earthquake (s rupture-scale varies cycle to cycle, and hence earthquake (s strength changes with time. The tendency of this variation has no necessity. On defining relative size of rupture scales, a statistical result shows that it is of the lowest probability that ruptures with the same scale occur in two successive cycles. While the rupture (s scale in the preceding cycle is (the probability of the following rupture (s) (small (, the probability of the following rupture (s) (large (is as many as 0.48. While the rupture (s scale in the preceding cycle is (middle (, the probability of the succeeding rupture being (small large (, the probability must be zero for the following rupture with (large (scale, and is 0.36 or 0.64 for the following rupture with (small (or (middle (sca le. The author introduces and improves the cascade-rupturing model, and uses it to describe the variability and complexity of rupture scale on individual fault portions. Basic features of some active strike-slip faults on which cascade ruptures have occurred are summarized. Basing on these features the author proposes principles of cascade-rupture segmentation for this type of faults of Western Sichuan, for its future cascade rupture, and further assesses the probable strength and its corresponding probability of the coming earthquake