Conventional terahertz (THz) waveform or spectral diagnostics mainly employ the electro-optic-based techniques or the multi-shot Michelson interferometer. Simultaneously, single-shot, ultrabroadband THz spectral measurements remain challenging. In this paper, a novel probe-free scheme based on the non-collinear autocorrelation technique is proposed to characterize the ultrabroadband THz spectrum at a single-shot mode. The non-collinear autocorrelator is a modified beam-division interferometer, in which the two beams are recombined non-collinearly onto a camera. The temporal or spectral resolution and range depend on the noncollinear configuration and camera parameters. This simple approach has been applied experimentally to characterize the ultrashort THz pulse generated from ultraintense laser-solid interactions, demonstrating the capability of single-shot ultrabroadband measurements without an auxiliary ultrafast laser probe. The proposed non-collinear autocorrelator here would be much useful for characterization and applications of low-repetition-rate intense THz sources and could also be extended to other frequency bands.