Journal of Digital Information Management Qianzhao Lei 10 5 2012 http://dline.info/fpaper/jdim/v10i4/6.pdf Such problems are often encountered in engineering designs: drawing moving targets orbits, however either there is no analytical formula of the orbit equation, or the derivation of getting a track equation is cumbersome; designing size of an equipment requires solving a complex transcendental equation. In order to address these matters, here were cited three instances, plotting the trajectory of a charged particle in a non-uniform magnetic field; drawing the spacecraft's orbit; designing the central axis size of an electrostatic precipitator cylinder. Through introduction of numerical calculation, the derivations of the orbits equations were avoided and the trajectories of a charged particle and the spacecraft were plotted respectively; solution of transcendental equation was found and the required dimension of an electrostatic precipitator cylinder in the design was got. So the numerical calculation plays a huge supporting role in engineering design.