To study the effect of (001) strain on energy band structure and optical properties of the simple orthorhombic Ca2P0.25Si0.75. The energy band structure and optical properties of the simple orthorhombic Ca2P0.25Si0.75 bulk under the (001) strain have been calculated by the first⁃principle pseudo⁃potential method based on density functional theory (DFT). The results show that the simple orthorhombic Ca2P0.25Si0.75 bulk is a direct semiconductor and the band gap value decreased with the tensile strain increased in range of 100%~116% and the compressive strain increased in range of 84%~88%, but it is increased with the compressive strain increased in range of 88%~100%. The optical properties have a significantly change by straining. The dielectric constant and the refractive index of the simple orthorhombic Ca2P0.25Si0.75 bulk are decreased when compressive strained increased, but they are increased as tensile strained increased. The reflectivity of the simple orthorhombic Ca2P0.25Si0.75 bulk moved to the high energy direction with the compressive strain increased, and it moved to the direction of low energy with the tensile strain increased. The absorption and the conductivity of the simple orthorhombic Ca2P0.25 Si0.75 bulk are increased with compressive strained increased. The transmission property of the energy band structure and optical properties of the simple orthorhombic Ca2P0.25Si0.75 bulk are changed by straining on the (001) surface. It is a useful method for modulating the photoelectric transmission property of the simple orthorhombic Ca2P0.25Si0.75 bulk.%为了研究（001）应变对正交相Ca2P0．25Si0．75能带结构及光学性质的影响，采用第一性原理贋势平面波方法对（001）应变下正交相Ca2P0．25Si0．75的能带结构及光学性质进行了模拟计算．计算结果表明：晶格（001）面发生100％～116％张应变时，带隙随着应变增加而减小；在晶格发生88％～100％压应变时，带隙随着张应变的增加而增加；84％～88％压应变时，带隙随着压应变的增加而减小．当施加应变后光学性质发生显著的变化：随着压应变的增加，静态介电常数、折射率逐渐减小，张应变则增大．施加压应变反射向高能方向偏移，施加张应变反射向低能方向偏移，但施加应变对反射区域的影响不显著．施压应变吸收谱、光电导率的变化与介电函数和折射率相反．综上所述，（001）应变改变了Ca2P0．25Si0．75的电子结构和光学常数，是调节Ca2P0．25Si0．75光电传输性能的有效手段．
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