When constructing small clear-distance tunnels in complex geotechnical conditions, there are many challenges including intolerable ground movement, face failure, and potential damage to adjacent tunnel. This paper focused on the study of small clear-distance shield tunnel construction in the typical upper-soft and lower-hard stratum. Numerical analyses are conducted to estimate the influence of the new tunneling on the existing tunnel. In addition, partition wall accompanied by cement-soil mixing pile is adopted as the control measure. The results demonstrate that the construction of the new tunnel has a big impact on the stability of the existing tunnel. The seal roof block should not be placed on the top region. The obviously influenced region of the existing tunnel agrees with the excavation diameter of the new tunnel, so monitoring in this region should be strengthened. Moreover, the safety control effect has been verified by numerical analysis and field test. This study provides a basis for the design and construction of tunnels with shallow buried depths and small clear-distances.