A sky luminance mapping system includes a camera unit, two pyranometer units and a processing unit. Camera unit includes a fisheye lens to shoot image of sky dome and is equipped with light-shading devices which block the sun from the camera unit corresponding to instant location of the sun at instant time. First pyranometer unit measures daylight illuminance from the sky dome and outputs first intensity signal while the light-shading device is applied to block the sun. Second pyranometer unit measures daylight illuminance from the sky dome and outputs second intensity signal without blocking the sun. A reference intensity value is obtained by subtracting a value of the first intensity signal from a value of the second intensity signal. According to the value of the first intensity signal and the reference intensity value, a total luminance of and the luminance distribution in the image of the sky dome are corrected.