Abstract: Combining with field tests of a typical section of No.312 national highway and indoor tests the subgrade tests have been done on the typical collapsible loess area in western China, in which the special soil are distributed in many places and bring out many questions on design and constructions of freeway.According to analyze the physic-dynamic parameter of foundation, the paper puts forward the regularities of collapsible loess before and af-ter handled by dynamic consolidation, acquires the basis parameters of dynamic consolidation.On the basis of tests, the impacting factors of compaction degree were studied.Results show that the relation between compaction degree and void-ratio is negative liner approximation.As compaction degree is more than 95%, the reasonable range of water content is to be controlled at 11.9%~15.4%, compaction soil is at -1~-5 m, the depth of 2 000 kN·m, 3 000 kN·m, 6 000 kN·m dynamic consolidation are seperately at 5~6 m, 6~7 m and 8.5~10 m, larger than which the effi-ciency of foundation reinforcement is not apparent.