The test flight of the gravity gradiometer survey system was taken in a flat area. In the future the tests will be carried out in rough mountain area and the topographic effect has to be taken into account. In this report the analytical downward continuation method was used to determine the gravity disturbance on the earth's topographic surface. The downward continuation is an improperly posed problem, especially in the processing of the aerial gradient data. In order to overcome this difficult, three methods were discussed and used for a simulated computation. The numerical computation shows that the gravity disturbance can be determined on the earth's surface with satisfactory accuracy. With a 1 Eötvös measurement error in the gravity gradient data, the gravity disturbance was determined on the earth's surface with the accuracy of 1 mgal. The gravity disturbance was recovered with the accuracy of 3 mgal when the measurement error of the gravity gradient was 5 Eötvös.