Alkyl hydroxamic acid was synthesized directly from coconut oil and hydroxylamine hydrochloride by hydroxylamine-coconut oil method under the catalysis of sodium hydroxide.The synthetic product was confirmed the existence of alkyl hydroxamic acid by qualitative detection using Fe3+ and analysising infrared spectra of coconut oil and products. The effects of the mass ratio of feed，reaction temperature，addition rate of NaOH and reaction time on the conversion rate of product were investigated.The results showed that the content of product could be up to 77.6%,when the mass ratio of feed was n（Coconut oil）：n（NH2OH•HCl）：n（NaOH）=1:3.30:7.26，the reaction temperature was 28℃，the addition rate of NaOH was 1.67ml/min and the reaction time was 8h. The new procedure has the advantages of not experiencing esterification with poisonous methanol，direct oximation,simple operation and environmental friendly.The alkyl hydroxamic acid was applied to low grade of phosphate floation and the good result was obtained that the concentrate grade of P2O5 was 30.55%,the recovery of P2O5 was 79.18%, tailings grade of P2O5 was 6.89%,which showed that the alkyl hydroxamic acid has a good selection performance. on the low grade phosphate rock flotation.