Abstract: Enhanced ion and plasma lines can be observed by the ground-based incoherent radar when high power HF waves were transmited into ionosphere. An ionospheric heating experiment was carried out in the fall of 2010, Norway. The long-lived enhanced ion and plasma lines were first observed in this experiment, and this may be caused by the Parametric Decay Instability (PDI). In addition, the VHF data show that the enhanced lines are descending in altitude with time during the heater-on period. The possible cause for the descending altitude may be the enhanced electron diffusion. In this paper, the reflection height is simulated based on the parameters of modified IRI and MSISE models, and results show that the reflection height can be descent with time due to the enhanced diffusion. A good agreement is obtained between the simulation and experiment, thus the hypothesis is proved to be reliable.