The invention provides a distance protection fault impedance computing method and system based on high frequency temporary state quantity. The method comprises the following steps: collecting cable data, wherein the cable data comprises high frequency harmonic waves in current and voltage at the position of distance protection installation and circuit unit resistance and inductance in cable data;according to the high frequency harmonic wave in current and voltage at the position of distance protection installation in cable data, calculating the distance percentage from a fault point to the position of protection installation; and based on the obtained distance percentage, in combination with the circuit unit resistance and inductance in cable data, calculating distance protection real fault impedance. The distance protection fault impedance is not influenced by transition resistance and fault position by extracting high frequency harmonic wave components in voltage and current after faults, and the calculation errors are superior to those in traditional schemes respectively; the more the harmonic wave components, the calculation result gets closer to the actual value; the length of a sampling window required by the high frequency harmonic waves is extracted, the action time of distance protection is promoted, and the method has good engineering practical value.