The test simulating contact explosion in saturated soil was completed in the φ2.5×5m pothole. Through the experiment, the data of the freefield in the saturated soil was obtained. The formulas of pressure, momentum and rise time with distance were fitted out based on a large number of test data. According to analysis of the test data, the spreading law of the wave in freefield of saturated soil was obtained. Theoretical analysis showed that saturated soil had the nature of liquiddynamic area appearing and shock wave forming when the stress wave spread in the saturated soil. The bilinear progressively increasingharding constitutive relation in saturated soil was established. Dividing pressure was determined and that was the value from shock wave to elastic wave. Moreover, the diving pressure related to media character was different in various soils. Because shock wave was formed easily, the structures in saturated soils had much higher risk of failure under the same explosive conditions.