With the continuous improvement and optimisation of the helically-coiled tube steam generator, it has been gradually applied in small reactors and become an essential heat transfer component in the reactor system. To enhance comprehension of the flow resistance properties of the helically-coiled tube steam generator and to supplement the inadequacy of the existing research, this work investigates the properties of flow resistance in helically-coiled tubes using helically-coiled heat transfer tubes as subjects of investigation both theoretically and experimentally. The experiments are conducted under pressure conditions ranging from 3 to 7 MPa, with mass flux between 200 and 1000 kg/m2s, and heat flux varying from 150 to 600 kW/m2. The coil diameter of the two sets of helically-coiled tubes are measured at 164 mm and 340 mm, respectively. The impact of thermodynamic and structural parameters on the resistance characteristics of single-phase and two-phase flow within helically-coiled tubes is examined, and new friction resistance correlations are introduced according to the experimental findings. Comparisons with empirical friction resistance correlations established in recent years reveal that the predicted results of the new friction resistance correlations that align most closely with experimental results. These findings provide valuable data and theoretical insights for the design of steam generators and their engineering applications.