Due to the environmental constraints, the overlapping singletube mined tunnels of 3C contract section of phase 1 of Shenzhen Metro, i.e. the north portion of GuoLao section, go through underneath the high building of Baihuoguangchang. During the tunnel construction, active underpinning construction technology is adopted for the pile foundations under which the tunnels go through. Due to the 1800t maximum axial force of the pile foundations to be underpinned, there exist great construction difficulties and great risks. Proper construction schemes and engineering countermeasures are taken in order to ensure the safety of the building. The paper presents the construction technology for the underpinning of the pile foundations applied in the construction of the overlapping tunnels.