The invention provides an equivalent model, a calculation method and a frequency analysis method for harmonic impedance at an inlet end of a direct-current line. The equivalent model comprises a current converter, alternating-current system impedance and an alternating-current filter, and is characterized in that the current converter is equivalent to a current converter model formed by two commutation inductors L3p which are connected in series; the alternating-current system impedance is equivalent to inductive impedance Zac; the alternating-current filter is equivalent to RLC series-parallel capacitive impedance Zacf; the RLC series-parallel capacitive impedance Zacf is connected with the inductive impedance Zac in parallel and is then connected between the two commutation inductors L3p in series; a first non-series end of each commutation inductor L3p is connected with the direct-current line; and a second non-series end of the commutation inductor L3p is connected with a grounding electrode lead. The equivalent model provided by the invention solves the technical problems that a current converter model in a high-voltage direct-current circuit harmonic impedance analysis equivalent model contains converter transformer casing stray capacitance, the complexity of the circuit is increased, an analytical expression of the corresponding equivalent impedance is difficult to be derived, and the harmonic impedance at the inlet end of the direct-current line cannot be derived through calculation.