In order to improve the wave-dissipating performance, a new grille plate-type open breakwater is presented. Based on flume experiments, the wave-dissipating performance of this breakwater was analyzed, and the influence of parameters, including the relative spacing between the upper and lower plates and the gap ratio of the grille plate, on the transmission coefficient and reflection coefficient were investigated. The results show that the wave-dissipating performance of this breakwater is satisfying, and it is better when the breakwater is above the still water level than when the breakwater is submerged; the transmission coefficient of this breakwater decreases with the increase of relative plate spacing; and the breakwater performs best at a gap ratio of the top and bottom plates of 0.1.