Airborne ocean colour remote sensing urgently require wide angle and large relative-aperture hyperspectral imager.Based on the research objective of wide angle and large relative-aperture,an airborne hyperspectral imager optical system was designed using an off-axis two-mirror anastigmat telescope and a modified Offner spectrometer.The field of view of hyperspectral imager was 40°,relative-aperture was 1/2.2,and working waveband was from 0.4 μm to 1μm.Relative aperture and image quality were improved by inserting a concentric meniscus in a classical Offner spectrometer.Ray tracing,optimization and analysis were performed by ZEMAX software.The analyzed results demonstrate that the MTF for different wavelengths is more than 0.67 at Nyquist spatial frequency 28 lp/mm,both smile and keystone are less than 6.5% of the size of pixel.It is easy for spectral and radiation calibration.The design results satisfy the requirements of specifications,the volume is small,mass is low,and is suitable for airborne remote sensing.