A benzimidazole-based fluorescent molecular probe phenyl-1,4-bis [(carbamoylmethyl)-1-pentylbenzimidazole hydrochloride)][M] was synthesized by using p-phenylenediamine, chloroacetyl chloride, benzimidazole and 1-brompentane as raw materials, yield 80.1%. Structure of M was identified by nuclear magnetic resonance spectroscopy and infrared spectroscopy, studying its determination of anions in aqueous solution(HEPES buffer solution, pH=7.4) by fluorescence spectroscopy. The results indicated probe M displayed rapidity, high selectivity, directness for the determination of phosphate inos, the addition of 9.0?0–4 mol/L PO43– in the 1.0?0–5 mol/L M solution led to a 36 nm red-shift in fluorescence maximum, an fluorescence enhancement, and M recognizes phosphate inos without interference from other common anions. All date show that M is a kind of good fluorescence materials.