The strata settlement caused by shield construction in crossing tunnels has influence on the deformation or even damage of the existing tunnel. Therefore

the stochastic medium theory is presented to calculate the existing tunnel settlement caused by shield construction in crossing tunnels

and to analyze the principles. The fundamental equations of the stochastic medium theory is applied to the crossing tunnels engineering. The stochastic medium model of the settlement of the existing tunnel resulting from shield construction in crossing tunnels is established

and the choice of parameters for calculating was discussed. The analysis for engineering example showed that it is very effective to calculate the settlement of existing tunnel caused by the shield construction in the crossing tunnels with the stochastic medium theory. The research has certain guiding significance to the shield safety construction in crossing tunnels.