The present invention discloses a tunnel toxic-and-harmful-gas deep-hole detection device and method. The tunnel toxic-and-harmful-gas deep-hole detection device comprises a detector, a lifter, and a control terminal, which are sequentially connected. The control terminal controls the lifter to achieve movement of the lifter. The detector comprises a shell with a hollow interior and two opened ends. An air inlet is formed in the outer wall of the shell. A gas detector and a gas sampler are arranged in the shell, and the air inlet is located therebetween. The tunnel toxic-and-harmful-gas deep-hole detection method comprises two steps, namely a gas detection step and a gas sampling step. The present invention can effectively detect components and concentrations of various gases in a drill hole, wherein the detection data is real-time and accurate.