Through numerically simulating the hypersonic reentry flow with ablation of carbon-phenolic heat-shield, the effects of ablation and pyrolysis on the thermochemical properties and electron densities of the flowfield were analyzed. 19 chemical species were considered and a two-temperature model was taken to describe the thermal nonequilibrium. The Navier-Stokes equations of thermochemical nonequilibrium flow coupled with the ablating boundary condition were solved to obtain the steady-state solution of the flowfiled. The effects of ablation were shown in comparison with the non-ablating baseline case, which has a non-reacting, non-catalytic wall and equilibrium radiation wall temperature. The method to determine surface chemical composition of the pyrolysis gas was discussed, and the effects of the pyrolysis ratio were investigated. The simulation and analysis performed on RAM-C model at flight speed of 7.65km/s and altitude of 61km or 71km show that, the dominant ablation and pyrolysis species are CO, H₂ and H, and both the ablation species and the effects of ablation are limited to the boundary layer. The mass fractions of atoms and ions decline as a result of ablation and this may result in the decrease of the peak values of electron density when they appear in the boundary layer. Furthermore, the ablation effects become more pronounced as the pyrolysis ratio rises, and the effects extend further into the flowfield with increasing distance from the stagnation point or with higher flight altitude.