The structural,electronic and optical properties of BN(5,5) nanotube under high pressures were studied by means of quantum-mechanical calculations based on the density functional theory and pseudopotential method. It was found that the geometric structure has large distortion under pressures. Differences exist between BN(5,5) nanotube and zinc blende structure BN: firstly, the band gap of BN(5,5) nanotube increases with pressure with a slope of -0.01795eV/GPa; secondly, the absorption spectrum does not “blue shift”, but stretches in the direction of infrared； yet these two structures have same electronic transfer direction. The electron density map indicated that BN(5,5) has stronger ionicity, which weakens with pressure increasing.