Smoke control technology is crucial in the risk management of fire in underground confined spaces. In this study, the integrated foam smoke reduction device (FSRD) of “foaming–spraying” is proposed in response to the challenging problem of smoke control of fire in underground confined spaces. The overall structure of FSRD device is designed and optimized through the numerical simulation of the internal flow field and experimental research. The optimal basic parameters are as follows: area ratio (R_m) of 20.25, pitch-to-diameter ratio (R_td) of 1/3 or 5/9, and throat diameter (d₃) of 18 mm . Additionally, the throat–nozzle distance (L_t) is 12 mm, and the operating pressure (p₀) is 3.0 MPa. Finally, the smoke reduction experiment verified that the FSRD designed in this study had a better effect of elimination than fine water mist and cylindrical foam jet, with the elimination efficiency reaching 36.73%. This study provides a new device for smoke reduction in controlling fires in underground confined spaces.