The mechanical behaviour of shield tunnel construction beneath adjacent existing highway tunnel is studied by using three-dimensional finite element numerical simulation method. The research demonstrates that it is dangerous to increase jack forces of the shield machine across adjacent upper existing highway tunnel which is considered as a kind of unloading structure. In addition

the jack forces of the shield machine is needed to be drop down to the limit value at 6 m distance from the edge of upper existing highway tunnel and the measurement of the existing highway tunnel floor is enhanced in advancement process of shield machine to guarantee the safety of upper existing structure.