The determination method of sample quantity of tunnel norm according to experience can not meet the new requirements of highway tunnel. The reliability of norm compilation can be improved by deciding the optimal sample quantity of original data. According to complementary budget norm of a highway tunnel and partition of norm items, classification of specific items and working items of construction processes in JTG/TB 06-02—2007 Highway Engineering Budget Norm,the improved statistical model is brought in and the optimal sample quantity of determination process of highway tunnel norm is divided into 3 kinds. The optimal sample quantities and their variation characteristics of the 3 kinds of highway tunnel norm are obtained. The results can provide reference for determination of sample quantity of original data of tunnel norm in the future.