According to the fact that yield or failure of soil around anchor rods is the main failure form of the rods,based on elastic and plastic limit equilibrium theory,considering soil stability under the most unfavor- able conditions,it is proposed that the single anchor destruction form in the air slake terrain and soil layer is the tapered sharing failure that engendered by the soil around anchor.Supposing destruction form for single line of anchors is triangular prism and half taper composed destruction model,formula to calculate the bearing ca- pacity of ground anchors is developed.

A calibration test was done in order to measure its sensitivity coefficient by an improved soil test derice. The experimental result shows that the soil pressure min-sensor made of the monocrystalline silicon (SPM-MS) is proved to be good linear, high precision and less discrete that can fetch precise data in low pressure range even near by O point, which guarantees the reliability of the soil pressure test in geotechnical engineering.