The invention provides a harmonic traceablility method for determining a user side as a primary harmonic source on the basis of impedance constraints. The method comprises the following steps: voltage and current waveforms at a point of common coupling (PCC) with harmonic pollution are acquired, and harmonic frequency which has a quite high content and needs harmonic traceability is found out, and contributions of two sides to harmonic voltages at the PCC are obtained; according to impedance intrinsic characteristics of the two sides, strict inequality conditions which need to be satisfied when it is determined that the user side is the primary harmonic source are simplified; through harmonic voltage and harmonic current measurement information at the PCC, all parameters in inequality constraint conditions can be directly or indirectly obtained; and according to properties of impedance at the two sides and the scope of a harmonic voltage current included angle at the PCC, the corresponding inequality constraint conditions are selected, and the inequality constraint conditions are satisfied, it can be determined that the user side is the primary harmonic source. The method can be applied to solving the harmonic traceability problem of determining whether the user side at the PCC is the primary harmonic source and has quite high engineering practicality.