By comparing the measured and model-calculated P absorbed by seedlings, the verification error sources and improvement of several mechanistic models of nutrient uptake in the process of P absorption by maize and soybean under different soil conditions were studied. The results showed that: (a)all of the three kinds of selected models can reflect the changing trend of P uptake by seedlings of Maize and soybean, (b) among the three selected models, the predicting ability of SC model is the poorest, and that of C2 model including the effect of root hairs is the strongest, (c)the most important factor influencing model's predicting ability is soil P level, and the model's predicting ability will become poor evidently when soil P level lowers, (d)by choosing the b2 model parameter, the root-mediated P activation and absorption could be included to a certain extent in the simulated P uptake by seedlings, and therefore the ability of selected mechanistic model based on numeric solution to predict P uptake by seedlings under p-stressed situation is enhanced, (e) the correcting equation for simulating deviation of the model based on analytical solution can markedly improve its predicting ability. \;