The conventional control strategies of shunt active power filter (SAPF) normally focus on the compensation for local non-linear loads, which may become uneconomical with a number of distributed non-linear loads. For an optimised network-wide harmonic suppression method, harmonic power flow calculation is the basis, and non-linear load modelling is the key which affects the accuracy and efficiency. First, this study discussed an accurate, but complicated non-linear load model, the coupled admittance matrix model for a typical harmonic source, phase-controlled rectifier, in detail, and proposed a fast calculation method which can simplify the calculation process evidently and explain the variation rules of model parameters clearly. Second, the main harmonic coupling characteristics of the rectifiers are analysed based on the calculation method, thus the rectifier matrix model is simplified and then an impedance-based network harmonic model for networks with distributed rectifiers is established. Finally, based on the network model, a promising control strategy of SAPF for network-wide harmonic suppression is presented, by which network parameters are acquired by online impedance measurement technique and good compensation performance is assured by the proposed network model. Experimental results and simulations are provided to validate the effectiveness of the proposed methods.