To prevent the waterrich soilstone composed strata at entrance of a plateau railway tunnel from collapse, the process, causes, and mechanism of the collapse are examined in detail. The investigation results show that under the condition of hydraulic power permeation, the waterrich soilstone composed strata have a poor selfstability, and the reserved core soil and the crown is prone to shear damage and block falling, respectively, which will further lead to local instability or crown collapse. After scheme comparison, the technologies, such as tunnel face backfilling, local backfilling and grouting, and sectioned excavation and support, are adopted, and a composed consolidation support technology is innovatively proposed, which effectively consolidates the collapse section and prevents the followed surrounding rocks from collapse.