<p>Understanding the evolution characteristics of surrounding rock stress during the weakening of spatial constraint effect caused by continuous excavation of deep tunnels under support restraint is crucial for maintaining rock stability and ensuring construction safety. This study developed a large-scale photoelastic testing device capable of multi-mode loading and a simulation test apparatus that replicates the weakening process of spatial constraint effect in tunnels. Enhancements were made to the light source and stripe image acquisition system. This new system effectively overcomes many limitations in traditional photoelastic test systems and significantly advances the photoelastic testing technology in tunnel and underground engineering sectors. A large-scale photoelastic test was conducted on a deep tunnel to elucidate the evolution characteristics of the surrounding rock stress. The findings showed that as spatial constraint effect weakened, the principal stress increment in the surrounding rock at the tunnel sidewall exhibited a gradual decrease, while at the tunnel arch foot, it demonstrated fluctuations. Therefore, the reinforcement of the arch foot is particularly crucial. As the tunnel's spatial constraint effect was completely lost, the functionality of the anchor cables at the vault was fully utilized, leading to an increase in surrounding rock stress. The coupling load-bearing effect of the anchoring cable and the surrounding rock was significant. The surrounding rock stress at the tunnel haunch consistently increased throughout the entire process of weakening the spatial constraint effect.</p>