A graphene and phosphotungstic acid modified electrode (GO-PTA/GCE) was prepared by drop coating of graphene and phosphotungstic acid. The electrochemical behavior of theophylline(THEO) was studied on GO-PTA/GCE by cyclic voltammetry，and the influences of ratio of GO to PTA，amounts of GO and PTA，type and concentration of supporting electrolyte，and scan rate on the electrochemical behavior of THEO at GO-PTA/GCE were discussed by cyclic voltammetry. The properties of electrode surface were studied by the nyquist plots. The results indicated that，in 0.02 mol/L H2SO4 solution，there was an irreversible oxidation peak at 1.185 V on the modified electrode.The peak currents were linear with the square root of the scanning rate in the range of 100-800 mV/s，indicating that the electrode process of THEO was irreversible and controlled by diffusion. The electron number(n)，effective area(A) and diffusion coefficients(D) of THEO were calculated to be 1，0.116 9 cm2 and 6.675×10-5 cm2/s，respectively. Under the optimal conditions，the differential pulse voltammetric method was used to determine THEO. A good linear relationship between oxidation peak current and THEO concentration in the range of 6.0×10-7-1.0×10-4 mol/L was observed，and the detection limit was 5.5×10-7 mol/L. The method was successfully applied in the determination of THEO in water samples with recoveries of 92.6%-106.3%.