A high-pressure shock wave generated by a donor charge subjected to an underwater explosion can sympathetically detonate an acceptor. Experimental research is the most effective method of studying sympathetic detonation because information regarding pressure evolution, pressure peak, and bubble pulsing cycle can be obtained directly. In this study, a set of underwater sympathetic detonation tests were conducted to investigate the pressure characteristics and critical distance for the sympathetic detonation of a 1-kg TNT donor and acceptor charges. Following the experiment, the energy, pressure, and bubble pulsing cycle were empirically analyzed. The results indicate that the best transmission and safety distances for sympathetic detonation were 99.55 and 128.92 mm, respectively. The acceptor charges were partially detonated by the donor when the gap distances were 109.90 and 119.98 mm. The degree of sympathetic detonation can be determined by analyzing the energy, bubble pulsing cycle, and pressure evolution.