The pressure induced structural transition of NaBH 4 from β-NaBH 4 (tetragonal-P42 1c ) to γ-NaBH 4 (orthorhombic-Pnma) is investigated by ab initio plane-wave pseudopotential density functional theory method (DFT). The BaSO 4 -type structure of orthorhombic high-pressure phase is testified theoretically for the first time. The calculated transition pressure of β-NaBH 4 (tetragonal-P42 1c ) to γ-NaBH 4 (orthorhombic-Pnma) is 9.66GPa and the orthorhombic high-pressure phase is stable up to 30GPa. Our results agree well with previous experimental results and demonstrate that high-pressure phase transition from β-NaBH 4 to γ-NaBH 4 may occur at low temperature. At last, the pressure effects on the electronic structures of α-, β- and γ-NaBH 4 are discussed.