The invention relates to a method for metering harmonics or inter-harmonics with specified frequencies, and the method comprises the steps: carrying out the sampling of a measured voltage or current signal at a sampling period T, and quantifying the obtained sampling data; assigning the number of AC components as N, wherein the frequency value of each AC component is in first-order progressive increase, and is a positive number (f1, f2,...,fN) not which is not greater than 2*pi/T; calculating the DC components of a voltage or current and the harmonic or inter-harmonic components of an AC voltage or current through employing a pre-estimation-correction algorithm; and calculating an estimated amplitude value and phase angle of the harmonics or inter-harmonics according to the obtained DC components and the harmonic or inter-harmonic components. The method does not need the frequency values of the set harmonic or inter-harmonic components to be maintained in a specific relation, facilitates the analysis of the harmonic or inter-harmonic components of a detected signal, directly obtains the sine and cosine components of the harmonics or inter-harmonics through employing the pre-estimation-correction algorithm, does not need to calculate sine and cosine functions, reduces the calculation burden, and is easier to implement.