Abstract: This paper aims to improve the brittle fracture characteristics of cement soil and to study the engineering properties and mechanical mechanism of asbestos fiber reinforced soft soil. It adds the asbestos fiber into fly ash and cement soil. Thus it creates a new kind of composite soil and carries out a series of experiments on the new soil. In these experiments, asbestos fiber is added into fly ash and cement soil with different ratios(0%~9%),which results in different composite soil samples with different content of asbestos fiber. All of the composite soil samples are subjected to the direct shear test, the unconfined compression test, the diametral compression test and the scanning electron microscopy test(SEM).Thus the mechanical behavior and mechanism of fiber reinforced soft soil are illustrated. It is found that the combination of asbestos fiber and fly-ash cement can significantly enhance the strength and stability of soft soil and improve brittle fracture characteristics of cement soil. There is a range of optimal content of asbestos fiber regarding the enhancement of the strength value of the composite soil. This range is between 3%~6%. Other asbestos fiber content outside the range can reduce the enhancement effect.