New experimental measurements of signal coherence in shallow water are presented. For signals with Iow frequencies of about 500 Hz in iso-velocity shallow water with a silt-sand bottom and a water depth of about 45 tn,the vertical coherence has no distinct depth dependence at ranges of 18.5, 55.5 and 92.5 kin, but it has obvious range dependence. The horizontal coherence lengths are all greater than 40 wavelengths, and the time coherence lengths are all greater than 510s at these ranges. These experimental results show that a low-frequency acoustic field has strong spatial coherence and temporal stability in iso-velocity shallow water.