A coal uncovering construction method for blasting large cross-section gas tunnels includes: analyzing stress distribution characteristics in front of a tunnel boring working face, and then determining a thickness calculation model of a reserved rock wall based on a limit equilibrium theory; establishing a tunnel model, simulating a construction condition and analyzing a construction result, and determining a thickness of the reserved rock wall; and fixing a detonator through a fixed sand ring, fitting the detonator with a construction hole by adjusting an adjustable protective plate, then embedding the detonator into a blast hole, and blasting the detonator for tunnel construction. Furthermore, an extension ring is fixed between the fixed sand ring and the adjustable protective plate.