Using single-shot chirped pulse electric-optic detector technique, the absolute electric field intensity can be obtained by tuning the angle to 45°, which is between crystal axis of quarter wave-plate (QWP) and linear polarization direction of detection laser. With charge coupled device (CCD), the size of terahertz spot can be gotten by probe-pump measurement. The energy of terahertz pulse is calculated with the experimental results. An effective method of measuring the terahertz pulse energy is provided.