In order to calculate the effect on the beam caused by an irregular accelerator element, we have expanded and improved the Linear and Electrostatic Accelerator Dynamics Simulation(LEADS)code. To achieve better calculation precision, the element was divided into lots of equal intervals. In order to simplify the calculation process, a one-dimensional field is simulated and the Lorenz equation is used directly. A onedimensional field can be imported into the LEADS code. The heteromorphic quadrupole is invented and its field is simulated and optimized using the POISSON code. As examples, the effect on the beam caused by the heteromorphic quadrupole and octupole is simulated.