The fully nonlinear Boussinesq model, called FUNWAVETVD, was used to simulate wave flume laboratory experiment to study the propagation and transformation of infragravity wave over fringing reef under irregular wave conditions. Based on the validation of predicted significant wave heights of short wave and infragravity wave and mean water levels, the crosscorrelation analysis and wavelet bispectrum were adopted to investigate the generation and propagation of infragravity wave and the related nonlinear energy transformation respectively. The results suggest that the infragravity wave can get energy from the peak frequency band in front of the reef. As the water depth on the forereef goes shallower, the nonlinear interaction goes stronger, the bound wave grows and the significant wave energy transfers from the peak frequency to lower and higher frequency bands. The infragravity wave on the reef flat is mainly generated by the moving breakpoint mechanism, and the energy transformation only occurs between low frequency band at the end of the reef flat.