A symbolic method is presented for calculation of the weakly nonlinear distortion effect of operational amplifiers. To avoid complicated symbolic generation by considering all transistor nonlinearities, a simplified analysis method is adopted. This method identifies the nonlinearity of each amplifier stage by a low-order polynomial. The proposed symbolic method can derive analytical distortion results automatically without the need of going through lengthy signal-flow graph analysis. This method is applied to sweep analysis of the opamp distortion with respect to the external feedback elements, by which optimal selection of the parameter value can be determined at any given frequency. Remarkable speedup over repeated Spectre simulation has been observed.