Abstract: This paper is to find out the strain property,distribution and its variation of the saturated expansive soil during its shrinking and cracking process under the condition of dehydration.A one-dimensional model tank of 40cm long, 5cm wide and 3cm high was designed and used for the purpose.The tank was filled with the saturated expansive soil and three grating sensing fibers with 11 FBG sensors were buried into the soil to measure the strain at different positions.Based on the measured strains and their variation,the paper obtained the characteristics of soil stain distribution and its temporal-spatial evolution process,especially the strain distribution on and around the first fissures.It was found that,the soil shows global shrinkage initially with the reduction of soil moisture content.Afterwards,differentiation of the soil stains occurred,showing alternate distribution of tension and compression.At the edge of the maximal shrinking area,when the state of FBG sensors was changed from compression to tension,the first fissure would appear in the region of higher tensile strain and strain variation rate.Thus,the FBG sensing technology of high spatial resolution can be a new idea and technology used for the analysis of the whole shrinking and cracking process of the expansive soil,revealing the cracking mechanism of expansive soil during the dehydration.