This Paper introduces a new method of measuring solar constant on sun-synchronous polar orbit satellites. The method is different from the traditional tracing mode which is usually used to measure solar constant while satellite moving relative to the sun. The solar constant monitor is made up of three same absolute radiometers with 15° field-of-view which are mounted on one plane. The middle one makes 15° angle with respect to the other two. Because the angle between the orbit plane and solar meridian plane is stationary for sun-synchronous polar orbit satellites

We mount the plane with three absolute radiometers which parallel the solar meridian plane. Sometimes the sunlight overpass the field-of-view of three absolute radiometers respectively with its angle velocity when satellite moving in its orbit. Since in non-tracing mode the change of primary aperture area with angle is different from that of tracing mode. We use a simplified model in which the area variation with angle is expressed by cosine function in the range of -7.5° to +7.5°. Formula obtained by differential equation of thermodynamics of simplified model in nontracing mode is similar with that in tracing mode. The highest value which is only needed to record and trace when electric power replace light power is only 0.04% lower than that of tracing mode. The precision of our method could reach the same order as the tracing mode

but much simpler in structure and facility for measurement.