Continuously tuning electronic and magnetic properties of nanomaterials specially by applying an axial tensile strain is a promising route for construction of impending electronic and optoelectronic nanodevices. In the present work, Si doping and axial tensile strain were simultaneously utilized in exploring the structural and electronic properties of single-walled (6,0) Si-N , Si-B and Si-N,Si-B-doped Stone-Wales defective boron nitride nanotubes at M05-2X/6-31+G(d) level. Our findings demonstrate that the Si doping of SW-BNNT destroys the hexagonal BN network and alters the insulating feature of the SW-BNNT. Binding energies of Si-doped SW-BNNTs are estimated to be smaller than un-doped SW-BNNT and decrease continuously upon axial tensile strain. It can be estimated that the Si-doped SW-BNNTs and, in turn, their axial strained forms are more suitable than SW-BNNT one for photoconductivity applications. The unstrained Si-N,Si-B has a lower band gap than unstrained Si-N and Si-B . The results show that the axial tensile strain is not a suitable strategy to improve the conductivity of Si-N,Si-B , contrary to those found in Si-N and Si-B . In the second part of this work, sensitivity of strained and unstrained Si-doped SW-BNNTs toward NO gas is evaluated. The results show that the chemical adsorption of NO is thermodynamically favored in both strained and unstrained forms. Among the Si-doped SW-BNNT-NO complexes, Si-N,Si-B -ON1 and Si-B-NO2 complexes with adsorption energy of -32.7 and -33.3 kcal mol(-1), respectively, are thermodynamically more stable than other complexes. In addition, dispersion-corrected adsorption energies were evaluated at M05-2X-D3/6-31++G(d,p)//M05-2X/6-31+G(d) level of theory. The greatest charge transfer value and change in the band gap upon adsorption was predicted in all complexes. Thus, it is expected that Si-doped SW-BNNT could be a favorable NT for removing and sensing the NO gas.