The existence of voids behind the lining has always been a “pain point” in tunnels. In recent years, prestressed concrete linings have been so densely reinforced that voids cannot be accurately detected using a single non-destructive testing method. A standard model of Voids behind the lining with reinforcement parameters, concrete mix ratio, thickness and material inside the void consistent with the actual project was produced. Based on this model, ground-penetrating radar, impact echo and ultrasonic laminar imaging detection tests were carried out and typical mapping of the various methods was obtained. Combined with the applicability of the practical operation in engineering, combined non-destructive testing methods is proposed and verified in actual engineering. The results show that the combined non-destructive testing methods can accurately detect voids of lining, and can take into account the detection efficiency to meet the detection requirements of complex reinforced linings.