Abstract: The effect of each nested variate in a nested model is analysed.It is found that the forecast could benefit by nesting partial variates,and the effect of each variate is different. So, only the effectual variates should be chosen for boundary nest. According to this approach, a scheme of boundary neat is presented and applyed to the limited area model(TL10) nested with the global spectral model (T63). for forecasting tropical cyclone over the South China Sea.A few numerical prediction tests show that this scheme is reasonable and efficient.