This paper proposes a method for determining the degree of the fittingpolynomial in Separation of gravity anomalies by means of trend analysis. Thesingle anomaly can be fitted by polynomial of different degrees with the leastsquares method, and the degree of the polynomial fitting this anomaly can beEstimation by "distortion poinfon the curve representing relationship betweenvariance of fitting degree and degree of the polynomial. The superimposedanonaly is firstly roughly divided by upward Continuation of different heights,and then the degrees of polynomial can be Estimation respectively. Tentativetheoretical calculation shows that this method not only can be applied satisf-actorily to the single anomaly caused by an individual geological body, but issuitable to some extent to the superimposed anomaly brought about by seve-ral geological bodies as well.