The concentration of Preformed Particle Gel（PPG）could not be measured accurately by the regular test of polymer concentration. A new method of determining PPG content has been established, so as to ensure that plan optimization and field pilot test of heterogeneous combination flooding can be carried out successfully. The pretreatment condition of ultrasonic wave and centrifugal extraction are studied. Considering the property of nitrogen in PPG, the concentration of pretreatment PPG is measured by Chemiluminescent N-determining method. The results show that the optimal pretreatment conditions are obtained as follows: ultrasonic power of 500 W,ultrasonic time of 15 min, centrifugal rotational speed of 10 000 r/min, centrifugal time of 3 min and toluene as extractant. Under the conditions above and using the new method above, the relative error can be less than 4.0% of PPG concentration and the detection limit is 10 mg/L, fully meeting the requirement of the field application.