Abstract: Matrix suction and saturation in situ in an excavation slope at any highway in Hubei province were measured with thermal conductivity sensors and moisture probes for period of time in order to studey the effects of matrix suction and saturation on excavation slopes in unsaturated expansive soil area and their varying rules. Monitoring results show that matrix suction of excavation slopes has more change than that of natural slopes, and that great range of suction in expansive soil excavation slopes has an unfavourable effect on the stability. Field soil-water characteristic curveistic (SWCC) really reflects the variation and relation of matrix suction and saturation, and offers necessary parameters that determine the strength caused only by suction or its change, thus the calculation of unsaturated soil strength is greatly simplified. Permeability coefficient is derived from field SWCC, which is of significance for actual engineering.