Adsorption characteristics of magnesium atoms on phosphorus-doped single-walled silicon nanotubes (SWSiNTs) are studied using plane wave pseudopotential method with generalized gradient approximation based on density functional theory. Adsorption energies of magnesium atoms on pure,phosphorus-doped and deformation effects (compressive or tensile) (6,6) SWSiNTs are calculated. Bond and Mulliken population of both pure and phosphorus-doped SWSiNTs are also analyzed.It shows that covalent bond and ionic bond conexist in armchair silicon nanotube superlattices doped with phosphorus atoms by forming ionic bond of Mg-P and Si-P,and enhancing ionic bond of Si-Si. Adsorption energy of Mg atom on SWSiNTs are improved significantly by doping phosphorus atoms. Adsorption energy are also increased under compressive deformation at 0.25%,0.50%,1.00%,1.25% and tensile deformation at 1.00%,1.25%. It enhances adhesion of interface of silicon nanotubes as reinforce combined with matrix.