In a large-scale ultra-fast and ultra-intensity laser system, with the increase of spectral bandwidth and beam aperture, the spatiotemporal coupling distortion will become more and more significant. This effect will not only degrade the beam quality and reduce the focusing intensity of the laser, but also invalidate the conventional evaluation method for laser far-field parameters. A pair of beam-expanding lenses, which may bring spatiotemporal coupling distortion to an ultrashort laser pulse, is taken as an example. And the influence of spatiotemporal coupling distortion on laser parameter measurement is analyzed in detail. It shows that in an ultrashort pulse laser system, an ordinary beam-expanding lens-pair can reduce the far-field peak intensity dramatically, and the actual pulse duration in the far field is more than 10 times longer than that measured at the near field by a single-shot autocorrelator. In this case, the focusing intensity estimated by using the measured value of near-field pulse width will be one order of magnitude bigger than the real value. It is expected that the results will be helpful in the optimal design of a laser system, the accurate characterization of an ultrafast laser pulse and relevant physical experiments.