The relationships of forest interception with rainfall and canopy density have been studied by modeling.It was concluded that the forest interception of Picea crassifolia could be simulated precisely by the compound model of I=a(1-e~(-PC)) bPC which including canopy density factors. The parameter a(1.362 7)means rainfall adsorption capacity of canopy, and parameter b(0.183 5)means coefficient of evaporation of canopy regionally, all this explain the law of forest interception which composed of 3 physical courses:adsorption,soakage and evaporation. It was indicated too that the curve of forest interception with rainfall marked 3 phase such as descent quickly phase(interception rate of fall canopy density stands is more than 36.1% while rainfall is less than 25mm),descent gradually phase (interception rate is in 36.1 .4% while rainfall is in 5~25 mm)and stable phase(interception rate is less than 20.4% while rainfall is more than 25mm),which explain the relationships of interception with canopy geometry shapecharacteristics of Picea crassifolia. The mean interception rate of imperfect stands in periods of investigation is in 19.36%~23.96%,but that attend to 25.67% for perfect stands with fall canopy density. The stemflow is less than 0.1% and the mean value is less than 0.018 2% for the special geometry shape construction of canopy go against stemflow.