Retrieving forest parameters, such as forest height, biomass from polarimetric and interferometric SAR (Pol-InSAR) images has been investigated and well demonstrated via airborne experiments for different types of forest. Terrain slope is a factor that always prevents the wide application of SAR technique due to its slant-looking imaging geometry. It induces changes of backscattering intensity, polarimetric response, etc. Regarding Pol-InSAR forest height retrieval, the effects of terrain slope on retrieval accuracy have been analyzed. The relation between terrain slope and forest height retrieval bias was established through theoretical analysis and simulation procedures based on the PolSARpro software. Based on these results, a simple topographic correction method for forest height retrieval from Pol-InSAR images was presented. This method could alleviate forest retrieval error in rugged areas easily.