The effect of interaction of biochar and fertilizer (IBF) on nutrients of red soil, yield of mustard and fertilizer utilization rate was investigated. IBF experiments were conducted, the treatments included RFC treatment (both biochar and fertilizer were applied), RF treatment (only fertilizer applied) and control treatment CK (no biochar and fertilizer applied). The fertilizer application dosages were 100%, 85%, 70%, 55% of the regular fertilizer application quantity, which were correspondingly denoted as RFC0, RFC1, RFC2, RFC3 of RFC treatment and RF0, RF1, RF2, RF3 of RF treatment, respectively. The results showed that the nitrogen utilization rate of RFC3 was higher than those of other treatments. The nitrogen utilization rate, yield of mustard and the soil organic matter content of RFC treatments were averagely increased by 161.42%, 79.28% and 241.42% compared with those of RF treatments, respectively. The alkali-hydrolyzable nitrogen and available phosphorus contents of RFC3 were higher than those of RF0. Additionally, IBF planting pattern promoted mustard to adsorb and accumulate N, P, K effectively. In conclusion, biochar played an important role in nutrients adsorption and enrichment for mustard growth. The mechanism of yield increment and soil fertility enhancement could be explained that the IBF planting pattern brought the comprehensive amendment effect in the red soil and provided mustard with sufficient nutrients by biochar’s adsorption and fixation for nutrients, which made fertilizer and nitrogen fertilizer utilization rate increase significantly, although the application amount of fertilizer was very low in the experiment.