To measure the modulation transfer function (MTF) of near-infrared InGaAs focal plane arrays (FPA), an all-reflective Offner optical system is designed and fabricated, which consists of two co-axial spherical mirrors, operating as a 11 imager with F/#=4. After optimization at the FPA working wavelength 1.7 μm, a nearly diffraction limited field of view (FOV) up to 8 mm×30 mm is obtained. The MTF at a space frequency of 20 lp/mm (referring to the 25 μm×25 μm device′s Nyquist frequency) is above 0.8 in the FOV. After fabrication and calibration of the optical system, a Zygo interferometer is used to check its performance, finding that the root mean square (RMS) of wavefront error is about 1/20 wave at 0.6328 μm, and the MTF@20 lp/mm (0.6328 μm), is above 0.93. Then the measured wavefront data is inputted into CODEV to calculate the MTF at 1.7 μm. The result shows that, the value of MTF @1.7 μm,20 lp/mm is still above 0.8.