To investigate the motion and radiation backward symmetry of high-energy electrons in linearly polarized ultrashort ultrastrong laser pulses,the electron trajectory,the angular distribution of spatial radiation energy,and the histogram of the spatial frequency distribution is plotted with the aid of numerical simulation software,based on the framework of classical nonlinear Thomson scattering.According to the research,nonlinear Thomson scattering is significantly influenced by the initial phase of the laser when the laser pulse is only a few cycles long.Also,its moving trajectory and spatial energy distribution which have apparent correlations have a "triple-symmetric" property concerning the initial phase of driving laser.The cutoff of the high harmonic spectrum can reach 1×10⁶ω₀,and the symmetry of high harmonic amplitude peaks provides a feasible idea of the selection of laser parameters in actual experiments.The study also provides a viable approach to obtain the desired spatial angle distribution of radiation energy and high harmonic amplitude peak of inverse nonlinear Thomson scattering by initial envelop phase modulation of the laser pulse.