Abstract: According to the energy principle, the formulae for axial force and displacement are derived. The shear stress between grout and soil is computed by use of the elastic-plastic shear displacement model, and soil unloading because of large displacement is taken into consideration. An application method of the principle of the minimun potential energy in pressure-type anchor problem is presented. The solution to the energy equation is given. Through a case, the distribution of axial force, shear stress and displacement of pressure-type anchor under various load levels is analyzed, load-displacement curve is discussed, and the ultimate anchorage length is computed. The conclusion are: ① the pressure-type anchor is mainly in elastic state under most load levels, and it will soon reach the ultimate bearing capacity once it enters the plastic state; ② the anchorage body energy transfer theory, which takes soil unloading into consideration, gives an explanation of the ultimate anchorage length of pressure-type anchor.