In order to guarantee the construction safety and high efficiency of bench method in soft rock, the geometric parameters of bench method used in Zhongtiaoshan Tunnel is optimized and analyzed. And then, the numerical simulation method and site monitoring method are adopted; and the safety of primary support structure, stability of tunnel face and construction convenience are taken as references for optimization work. The analytical results show that: 1) The stress on tunnel primary support structure is rational and the construction machinery operation is convenient when adopting bench method for soft rock tunnel and the top heading length is controlled within range of 4-5 m. 2) The tunnel construction efficiency and the tunnel face stability can be guaranteed when the top heading height is 0.6H (H refers to height of tunnel crosssection); the top heading height should be in the range of 0.6H-0.7H when the tunnel is in bad surrounding rock (i.e. shallow bury or water inrush from Grade Ⅴ surrounding rock).