A pot experiment was conducted to study the effects of different levels of phosphorus (P) (0, 20, 80 mg/kg) and oxytetracycline (OTC) (0, 40, 160 mg/kg) on the biomass and root development of wheat and alfalfa seedlings. The results showed that at all OTC levels, the aboveground biomass of wheat in 20 and 80 mg/kg P treatments was greater than that when no P was added, being 22.7%~34.1%, 10.0%~30.0% and 9.1%~18.3% greater. Except for the 160 mg/kg OTC+ 80 mg/kg P treatment, root biomass of alfalfa in all treatments was less than that in the control without OTC and P, being 8.8% less. Root length and surface area of wheat decreased with increasing OTC level. Overall, P application significantly enhanced the aboveground growth of wheat, but had no significant effect on the growth of alfalfa. OTC inhibited root development of alfalfa. The results of the present study can provide a theoretical basis for evaluating the effect of soil OTC residue on seedling growth of crops and instructing proper application of P-fertilizers.