The present invention relates to an ellipsoidal passive millimeter wave imaging system. The ellipsoidal passive millimeter wave imaging system includes a millimeter wave radiometer array, a calibration system, a light collimating system, a data acquisition system, a computer processing system, a test background and a measured target; electromagnetic waves emitted from a human body are radiated on the first focal point of an ellipsoidal antenna through a radiation plate; the electromagnetic waves are reflected through the offset feed ellipsoidal antenna, and the reflected electromagnetic waves are received by the millimeter wave radiometer array composed of 70 millimeter wave radiometers located at the second focal point of the ellipsoidal antenna; the electromagnetic waves are processed by the data acquisition system and are transmitted to a computer; the reflection plate carries out scanning in a certain range of angles so as to acquire electromagnetic waves emitted by the measured target at different locations; and a plurality of sets of data are processed through an algorithm, so that an image can be obtained. The imaging system of the invention has the advantages of faster imaging, high real-time performance, more pixels, clearer image and better effects.