The slope at the entrance portal of Gaoyangzhai tunnel is high and steep and is located above national highway No. 318. It is very difficult to reinforce the slope. A combination of several slope reinforcement technologies is adopted, so as to ensure the safety of the vehicles on the national highway and the construction facilities and construction labors and to ensure that the reinforced slope can meet the stability and safety requirements of the railway in the longterm operation. The reinforcement technologies adopted are presented, and the plan of slope stability monitoring during reinforcement and the safety guarantee measures are described. Conclusions drawn are as follows: 1) The combination of the several reinforcement technologies adopted in the reinforcement of the entrance portal slope of Gaoyangzhai tunnel is effective; 2) Strict slope stability monitoring plan is performed, but no obvious slope deformations is found. The effect of such slope stability monitoring is limited. It is still to be determined whether such slope stability monitoring is applicable or not; 3) The route changing of the national highway is necessary. 