Abstract: Taking watermelon variety of ‘Jincheng No.5’ as the test material, a field randomized-group experiment included sole application of chemical fertilizer（T1）,sole application of bio-organic fertilizer（T2,equal amount of nitrogen with chemical fertilizer）,20% bio-organic fertilizer+80% nitrogen fertilizer（T3）,40% bio-organic fertilizer+60% nitrogen fertilizer（T4）,60% bio organic fertilizer+40% nitrogen fertilizer（T5） and no nitrogen fertilizer（CK） treatments were carried out to investigate the effects of partial substitution of chemical nitrogen fertilizer by bio-organic fertilizer on the growth, yield, quality and fertilization benefits, in order to provide reference for the rational fertilization and sustainable development of watermelon growing in gravel-sand mulched field in Ningxia.The results showed that length of main stem, diameter of main stem, number of leaves and leaf area index of watermelon were increased at different degree with the treatments of bio-organic fertilizer partial instead of chemical fertilizer and T5 was the most appropriate treatment for the growth of watermelon.At the same time, bio-organic fertilizer partial instead of chemical fertilizer increased the total yield and commodity yield of watermelon and the treatment of T5 achieved the highest total yield of 31.2 t·hm^-2 among the treatments, which raised by 55.1% and 46.6% compared with that no fertilization and sole chemical fertilizer.The bio-organic fertilizer substituted for N fertilizer improved the agronomic efficiency and fertilization efficiency of N fertilizer.Moreover, the seedling mortality and plant disease incidence were significantly decreased with bio-organic fertilizer partial instead of chemical fertilizer.Compared with sole chemical fertilizer,the soluble solids content in the center and at the edge of watermelon were significantly increased with bio-organic fertilizer partial instead of chemical N fertilizer（T5） by 12.7%and 11.5%,respectively.In a word,the treatment of T5 （60% N of bio-organic fertilizer+40% N of chemical fertilizer）was a suitable nitrogen fertilization strategy from the aspects of growth,yield,fruit quality,nitrogen agronomic efficiency and economic benefit for the local watermelon production.