A method for single-shot detection of ultrashort terahertz (THz) pulse based on wavelength coding is proposed. This method combines the new crossed and balanced electro-optic sampling technology and the wavelength coding technology, which has the advantages of both of them: it realizes single-shot real-time measurement for ultrafast THz pulse with high modulation depth and high signal-noise ratio. In order to achieve single-shot measurement, linear chirped laser pulses are used as the probe laser to map the temporal modulation of THz wave to the frequency domain, and the information of which is singly-acquired by spectrometers. In the aspect of electro-optic sampling technique, instead of the traditional wavelength coding single-shot measurement method, we use a novel crossed and balanced method. By setting two optical paths with a pair of equal and opposite static bias phases, the symmetrical push-pull modulation is achieved. The detecting linearity and modulation depth near 0° optical bias can be improved effectively, and the dynamical noise is suppressed.