Abstract: Disposing with topping and not topping in K326 growth duration, researching the change law of protease and nitrogen compound in fresh tobacco leaves. The result is show that: Protease and the total free amino acid submit " M " type curve in growth duration. and reached peak after topping 20d and 50d, the protease of topping is larger than not topping’s , but the total free amino acid is opposite. Soluble protein and non soluble protein show the tendency that reduces after going up first in growth duration, and reaching peak after topping 20d, reducing soon afterwards gradually, the Soluble protein and non soluble protein of topping is larger than not topping’s.