Abstract: The study aims to investigate the effect of selenium fertilizer on main quality index and selenium content of three medicinal herbs: Angelica, Dangshen and Astragalus in Dingxi, Gansu Province. Single factor randomized block design was used, selenium fertilizer was applied as basal fertilizer, and five selenium fertilizer treatments (0 (control group), 75, 150, 225, 300 kg/hm²) were set up. Main quality index and selenium content of the three medicinal herbs were measured under different treatments. The results showed that selenium fertilizer had significant influence on volatile oil and ferulaic acid of Angelica and astragaloside of Astragalus. The maximum astragaloside content was 0.138%, which was 42.3% higher than that of the control; the maximum ferulaic acid and volatile oil content of Angelica were 0.198% and 1.0%, and increased by 94.1% and 42.9%, respectively, compared to the control. Selenium content of the three kinds of traditional Chinese herbals was higher than that of the control under selenium fertilization. The maximum selenium content of Angelica, Codonopsis pilosula and Astragalus reached up to 1.26, 0.98 and 0.37 mg/kg, respectively. Comprehensively, selenium fertilizer could improve the quality and selenium content of the three studied medicinal herbs when fertilizer amount was 75-150 kg/hm².