A coumarin fluorescent probe [HDQ][P66614] were synthesized from Acid-base deprotonation reaction of 3-Chloro-7-hydroxy-4-methylcoumarin (HDQ) and quaternary phosphorin[P66614][OH] as raw materials, and characterized by 1HNMR, FTIR. Based on fluorescence spectroscopy, the detection sensitivity, selectivity and anti-interference experiments were carried out to investigate the low detection limit (LOD), specificity and anti-metal cation interference of Fe3+ of the probe [HDQ][P66614], and the detection mechanism was analyzed, and the application of the test probe [HDQ][P66614] for the detection of Fe3+ in actual samples was investigated. The results showed that HDQ, as a fluorescent signal group and a specific recognition group, complexed with Fe3+ at a ratio of 1∶4 to form a non-fluorescent complex. In the concentration range of 60~600 μmol/L, Fe3+ has a good linear relationship with the fluorescence intensity of probe [HDQ][P66614] solution, LOD=0.6 μmol/L. The probe [HDQ][P66614] was simple to synthesize, the response time of Fe3+ was 10 s, and the pH=2~12 range, the probe [HDQ][P66614] had a fluorescence quenching response to Fe3+, quenching is more pronounced when the pH is farther away from 7. The probe [HDQ] [P66614] showed specificity for the detection of Fe3+ and anti-interference ability for ten