The invention discloses a sheet micro-cavity near infrared seed light injection locking tunable intermediate infrared narrow line-width optical parameter amplifier which comprises main pump light, a seed light source, a sheet micro-cavity light optical parameter oscillator (amplifier) and a high-pass optical filter. The main pump light is a single-frequency nanosecond laser device with the wavelength of 1064 nm, and pump light can be outputted for integral systems by the main pump light; a seed light system comprises light beam shaping lens systems, and the main pump light with the wavelength of 1064 nm is subjected to frequency doubling by means of birefringence phase matching by the aid of lithium boric oxide crystals, namely LBO, so that the pump light with the wavelength of 1064 nm can be converted into a single-frequency seed pump light source with the wavelengths of 532 nm; an optical parameter amplification system comprises the single-frequency pump light source with the wavelength of 1064 nm, a beam combiner and nonlinear periodically poled crystals, and the seed light system is responsible for generating injection locking near infrared narrow line-width single-frequency seed light.