The damage analyses of breakwaters have an important guiding role for its rehabilitation or reconstruction. During the past 45 years of construction and operation，a rubble mound breakwater armored with Tetrapod units in the Mediterranean has damaged successively under strong wave conditions. Although it has been repaired many times，it still suffered local damage. In this paper，by field investigation，theoretical formula verification，and 2D physical model test，the damage reasons of Tetrapod blocks are analyzed. Results show that：1）The Mediterranean area has strong waves，high wave height，long period，long duration，and great destructive power. 2）The main reason for the breakwater damage is that the slope of the protective surface is too steep. 3）The unit placement quality also has a significant effect on the stability of the Tetrapod units. The stability of the Tetrapod units with randomly placed is much worse than that of the Tetrapod units with regular well placed. 4）For the breakwater projects in the Mediterranean，the factors of amour slope，block installation quality and unit placement density should be considered in the design.