Hydrogen-blended natural gas delivered via pipeline networks supports the development of hydrogen energy. However, hydrogen-blended natural gas containing water vapour significantly decreases delivery efficiency and accelerates pipeline corrosion, necessitating rigorous dewatering before transportation, storage, and utilisation. This mixture is primarily methane-based, with component variations depending on the source. This study employs Box–Behnken design (BBD) and particle swarm optimisation (PSO) to examine how the composition and content of hydrogen-blended natural gas influence the condensation rate in Laval nozzles. Utilising computational fluid dynamics (CFD), we calculated the flow parameters of various hydrogen-blended natural gas fractions and contents through the Laval nozzle. The optimal gas composition was identified using BBD and PSO, resulting in a condensation rate of 78.65% with CH4 at 69.212%, C2H6 at 2.028%, C3H8 at 1.107%, and H2 at 9.01%. This condensation rate is significantly higher compared to mixtures containing only CH4 and H2. These findings guide the investigation of phase transformation mechanisms in multi-component condensation of hydrogen-blended natural gas with water vapour and their engineering applications.