Abstract: The pressuremeter tests in pure clay and common clay are analysed separately in this paper. The yielding of the tests is classified intO two types according to the direction of the largest main stress when the soil begins to yield. The classification formula of the two yielding types and their limit linear pressures are given. Then the plastic zone is separated into two secondary areas according to the changes of the direction of the latgest main stress, and the stress field in each secondary area are deduced. At last, the calculating formulas of limit pressures are given and compared with the test values.