A novel “turn on” fluorescence sensor for H2O2 detection was developed based on boron and phenyl doped graphitic carbon nitride nanosheets(BP-C3N4) as peroxidase mimic.The BP-C3N4 with peroxidase-like activity were prepared by thermal polymerization of cyanamide with 3-aminobenzeneboronic acid followed by ultrasonic exfoliation.Similar to horseradish peroxidase，the BP-C3N4 could catalyze the oxidation of amplex ultrared reagent(AUR) by H2O2 to generate the resorufin with strong fluorescence.Parameters for the peroxidase like catalytic reaction，including response time，pH value and temperature were further investigated.Under the optimal conditions，the obtained fluorescence signal showed a good linear response to H2O2 concentration over the range of 0-100 μmol/L，with a correlation coefficient(r2) of 0.992 2 and a limit of detection of 1.1 μmol/L.The fluorescence sensor was applied in the detection of H2O2 residue in real samples，and the results were consistent with those of the existed method.