A flat-field spectrograph with self-scanning photodiode arrays detector is introduced. It is Czerny-Turner structure, spectral resolution is 0.5 nm per pixel. Wavelength calibration and radiance calibration method by using standard DC mercury lamp and tungsten lamp are described, with the spectrograph, 290～450 nm solar ultraviolet/atmosphere spectrum is measured and the measured results are given. Characteristics of detector is discussed. In order to restrain influence the temperature drifting on measuring result, some pixels at the two ends of CCD array are masked with mechanic structure, they are looked as background reference pixels, just as dumb elements. Real-time background subtracting restrains the impact of temperature drift and dark current and dark noise. According to the structure of instrument, the influence of the slit width on spectral line is discussed, the relative measurement error of instrument is also analyzed.