Abstract: Tunnel construction in loose and mixed soil layer has engineering problems such as large deformation of surrounding rock and large ground subsidence, which affects construction safety and normal use of other structures. This article first systematically analyzes the engineering characteristics of the loose and mixed soil layer and its impact on tunnel construction safety. On this basis, a comprehensive treatment measure is proposed for tunnels in the loose and mixed soil layer, which combines the reinforcement of double-sided wall guide pits with the reinforcement of rotary jet pile foundations. Numerical simulation is used to quantitatively analyze the stress evolution and deformation characteristics of the tunnel during the construction process. The results show that the reinforced double-side heading method can effectively control the horizontal and vertical displacements of the tunnel structure, and the maximum displacement meets the requirements of the engineering limit. The initial support system shows good bearing capacity, and the structural principal stress level is maintained in a low range. The safety factor of the tunnel reaches 2.0, and the crack width is controlled within 0.2 mm. All indicators are better than the specification requirements. The research results effectively solve the problems of large deformation of surrounding rock and surface settlement control in tunnel construction in loose and mixed soil layer, which can provide reference for tunnel construction under similar complex geological conditions.