The design of sensors for detecting formaldehyde (HCHO) gas in the environment is vastly necessary since even at low concentrations, it is very harmful to human health. Herein, a novel, reproductive, selective, and sensitive HCHO sensor has been designed by functionalizing SnO2 with beta(12)-borophene sheets for the first time via density functional theory calculations. The results revealed that the wide direct band-gap SnO2 semiconductor and zero-band-gap beta(12)-borophene form a distinctive orbital hybridization heterostructure with a moderate direct band gap of 1.09 eV and effectively enhance the electrical conductivity, selectivity, long-term stability, and the HCHO molecule response. The HCHO molecule chemisorbs in several orientations on the beta(12)-borophene/SnO2 surface, behaving as a charge acceptor and donor at some point. Moreover, applied biaxial strain and external electric field enhance the stability, band gap, and charge transfer of the adsorbentadsorbate interactions. Therefore, a beta(12)-borophene/SnO2 sensor with excellent adsorption, work function, tunable band gaps, charge redistributions, and sensing properties can be applied in indoor pollution detection and optoelectronic applications, where an external electric field can be used.