Harmonics and filters are very important for technics and economics in HVDC transmission engineering. The digital computer programs are new forceful tools for engineering studies. A general digital program for engineering has been developed. It has been used for several filter projects in China. We can use it to calculate:（1） The harmonic voltage and voltage distortion at every node of power network.（2） The telephone interference factor in the overhead line of power network.（3） The Harmonic current through branches of power network.（4 ） The electric loads of filter element （including the fundamental andharmonic） （ 5 ） The impedance-frequency characteristic （Table or/and drawing） .