In order to obtain accurate signal to noise ratio (SNR) measurement of picosecond ultrashort pulse and enlarge the range of pulse SNR measurement, a repetition frequency scanning third-order correlator is built, which considers the problem of parametric fluorescence induced by ultrashort high-power laser pulses in correlated process. Besides, the measurement technology is carried on picosecond short-pulse optical parametric chirped pulse amplification (OPCPA) pump source. The results show that the impact of parametric fluorescence on the measurement is largely eliminated by large-angle noncollinear phase matching, furthermore, by reducing the background noise the dynamic range can achieve about 107. Because of the asymmetry of cross-correlation technique, the correlator can also analyze temporal profile. The results indicate that pulse front edge is coincident with sech type curve, and pulse back edge has good agreement with Gauss type curve.