A differential pulse voltammetric（DPV） method was developed for the detection of phoxim based on solid liquid microextraction on nanoparticle cobalt hydroxide in situ modified carbon paste electrode.Phoxim was detected by with nanoparticle cobalt hydroxide in-situ modified carbon paste electrode.Under the applied potential,phoxim molecules were extracted onto the electrode surface,which interacted with cobalt hydroxide to form a complex and result in an irreversible reduction peak at-0489 V.The reduction peak current increased linearly with the increase of scan rate,indicating that the reduction reaction was controlled by surface adsorption.The extraction behavior followed a Temkin isothermal adsorption model.The relationship between pH and potential showed that the reduction process was just a reaction of an electron with a proton.Electrochemical impedance spectroscopy（EIS） and quantum chemical method were used to prove that the reduction reactions could occur spontaneously,while the calculation results were consistent with the experimental results.The system was used to detect phoxim.There existed linear relationships between the reduction peak current and logarithm of phoxim concentration in the ranges of 3.333×10-13-3.333×10-8 mol/L and 3.333×10-8-3.333×10-6 mol/L.The limits of detection（S/N=3） was 3.333×10-13 mol/L.With good reproducibility and selectivity,the method was applied in the determination of phoxim pesticides in spinach with satisfactory results.