In order to study the effects of topographic inhomogeneity on wave breaking process，a series of experiments were conducted with normal，oblique and multidirectional irregular waves breaking on three-dimensional lens topography to study the breaker indices. The existing formulas of wave breaking on two-dimensional topography were compared with the experimental results to study the differences of breaker indices of the two topographies. The results showed that the values of breaker indices of three-dimensional lens topography were larger than the calculated values，which was caused by the wave focusing effect of lens topography. Further，the general forms of existing formulas were used to fit the experimental data and the parameters in the calculation formula of the crushing index suitable for three-dimensional lens topography were given. The results can provide the basis for engineering designing.