With the technological advantages of high thrust, high specific impulse, long life, variable specific impulse, and high efficiency, the variable specific impulse magnetoplasma rocket engine has become the essential advanced propulsion system for the deep space exploration and manned space flight in the future. In the variable specific impulse magnetoplasma rocket engine, the ion cyclotron resonance heating stage is linked with the helicon plasma source. The operation status of the helicon plasma source has a direct influence on the ion heating process in the ion cyclotron resonance heating stage. It is of great significance for the testing and the optimization of the engine performance to reveal the influence of the ionization process on the ion heating process. In this paper, a multi-fluid model in which the ion cyclotron resonance heating stage is linked with the helicon plasma source is developed. The numerical simulations with different input currents of helicon plasma source and different pressures are performed to analyze the effect of the operation status in the helicon plasma source on the ion energy density in the ion cyclotron resonance heating stage. The results show that the discharge mode of the helicon plasma source gradually changes with the increase of the input current and that the plasma density jump appears while the ion temperature remains basically unchanged. With the plasma density jump and nearly identical ion temperature the ion energy density jump also appears in the simulation domain. Similar to the results of the simulation under different input currents of the helicon plasma source, the plasma density and the ion energy density also jump when the pressure increases. However, the ion temperature decreases due to the discrepancy between the input frequency and the resonance frequency. With the numerical model and the input conditions of this study, the ionization process in the helicon plasma source is decoupled with the ion heating process in the ion cyclotron resonance heating stage. The energy gain of a single ion in the ion cyclotron resonance heating stage does not change with the operation status of the helicon plasma source, thereby accounting for the ability of the engine to work in multi mode.