Temporal contrast (TC) is one of the most important parameters of an ultrahigh intense laser pulse. The third-order autocorrelator or cross correlator has been widely used in the past decades to characterize the TC of an ultraintense laser pulse. A novel and simple single-shot fourth-order autocorrelator (FOAC) to characterize the TC with higher time resolution and better pulse contrast fidelity in comparison to third-order correlators is proposed. The single-shot fourth-order autocorrelation consists of a frequency-degenerate four-wave mixing process and a sum-frequency mixing process. The proof-of-principle experiments show that a dynamic range of ～10¹¹ compared with the noise level, a time resolution of ～160 fs, and a time window of 65 ps can successfully be obtained using the single-shot FOAC, which is to-date the highest dynamic range with simultaneously high time resolution for single-shot TC measurement. Furthermore, the TC of a laser pulse from a petawatt laser system is successfully measured in single shot with a dynamic range of about 2 × 10¹⁰ and simultaneously a time resolution of 160 fs.