With the theory of runoff yield at natural storage and the computed restore method at separate layers, the variation law of the precipitation infiltration recharge with groundwater depth was investigated by using the measured data from the lysimeter in 8m fixed-depth at Ranzhuang. The genetic-mechanism of optimal depth and stable points was revealed. Under the test condition, the optimal depth is about 3m, the precipitation infiltration recharge decrease with the groundwater depth increasing, which approaches stability at 6m depth.