With the continuous construction of underground engineering projects, it is inevitable that new tunnels will occasionally cross parallel to existing tunnels. During shield tunneling, the rate of soil loss from different strata significantly affects surface displacement and tunnel deformation. This study, based on the Beijing Airport Line Metro project, designed two sets of parallel tunnel crossing models with soil loss rates of −7% and + 2%, respectively, and conducted experiments using the soil pressure balance shield tunneling test platform at Beijing University of Technology. An automated monitoring system recorded real-time data on the excavation quality of the shield machine, cutterhead torque, screw conveyor torque, as well as surface displacement, strain in the existing tunnel, and soil pressure. The experimental results indicate that with a negative soil loss rate, the disturbance to the soil caused by shield construction is more pronounced, resulting in a wider surface settlement trough with a settlement value 2.6 times greater than when the soil loss rate is positive. Additionally, the additional soil pressure at the arch waist on the left side of the existing tunnel increased by approximately 20%, with a variation magnitude 2.55 times greater than the positive condition. This suggests that under negative soil loss conditions, the existing tunnel is more susceptible to deformation and even failure.