The national standard of pulse waveform parameter based on the NTN technique cannot fully meet the measurement and calibration requirements of the current ultra-high speed electrical pulse waveform. We structure the pulse waveform measurement system based on electro-optic sampling technique and independently design and prepare the high frequency LiTaO3-based electro-optic modulator with coplanar waveguide structure. The 3 dB frequency of the modulator measured by the network analysis system can reach 100 GHz. We optimize the system parameters by analyzing the experimental results of the output pulse waveform of photodetector. On the basis of the above optimization and improvement, we finally achieve the precise measurement for the electric pulse waveform of 70 GHz high-speed photodetector, and the rise time and full width at half maximum of the measured waveform are 4.6 ps and 5.0 ps, respectively. It will give reference for the establishment and sustained promotion of the national standard pulse waveform parameters of our country based on the electro-optic sampling technique.