Using compressive sensing for imaging has many applications,and it is an important branch of computational imaging.In this Letter,freeform surfaces are introduced in the hardware optical system design of a compressive sensing imager.The system works under the medium wave infrared band and realizes a 16× compression with a field-of-view of 7.5° × 6°.Good imaging performance is achieved in both the entire system and the freeform objective optics.Compared with the system using all spherical lenses,the volume of the freeform system is about 1/3 smaller,and the total transmittance is about 56％higher,which shows the benefits of using freeform surfaces for compressive sensing and computational imaging.