Affected by geological conditions, design and construction, and operation level, highway tunnels put into operation generally have different forms of defects. Among these, lining voids constitute a primary defect in the lining, posing significant threats to the safety and stability of tunnels. Consequently, this paper focuses on highway tunnels with typical lining defects, specifically voids behind the lining, as the subject of investigation. The numerical model was established to examine the impact of lining voids in different directions on the mechanical properties of the lining. Additionally, the cohesion zone element method (CZM) was introduced to quantitatively analyze the cracking mechanism and crack distribution patterns in highway tunnel linings with voids oriented in various directions. According to the results: (1) The voids lead to areas of concentrated tensile stress in the lining structure. As the void area expands, the tensile stress region in the lining increases, significantly compromising the overall safety of the lining structure. (2) With an enlargement of the void area, there is an increased incidence of damage to the lining element. (3) The impact on stress and crack distribution within the lining structure is more pronounced when the void area is increased along the tunnel’s longitudinal direction compared to when it is expanded in the tunnel’s circumferential direction.