During the operation of nuclear reactors, corrosion particles originating from various materials progressively accumulate on the surfaces of the heat transfer tubes in the steam generator, thereby inducing fouling. This fouling not only diminishes the heat transfer efficiency of the heat exchanger but may also result in pipe blockage. A comprehensive fouling deposition model was developed for the entire secondary side of double-side heating once-through steam generator (OTSG) with helical tubes. The influence mechanisms of heat transfer characteristics and flow patterns within the heat transfer zone on surface fouling were systematically investigated, and the distribution patterns of fouling on the heat transfer tube surfaces of the OTSG secondary side were elucidated from multiple perspectives. Furthermore, an in-depth analysis of the internal fouling distribution characteristics was provided. The findings indicate that the unique crescent-shaped flow channel structure of the OTSG induces circumferential non-uniformity, leading to a spiral distribution of fouling on the heat transfer tube surfaces. Additionally, the circumferential non-uniformity of fluid velocity or quality in different heat transfer regions significantly affects the circumferential fouling distribution. Moreover, variations in reactor operating conditions influence the spiral band distribution of fouling. As power levels increase and the inlet flow rate on the secondary side rises, the extent of the spiral band distribution of fouling becomes more extensive, and its characteristics become more pronounced.