We investigated a structure,which is made of many unit cells.There are two kinds of dielectric layers in each unit.The inside structures of adjacent cells are slightly different.However,we keep the size of each cell being the same.Surprisingly,we find that the width of the photonic bandgap of such a structure is very large.It is over 2 times larger than that of ordinary photonic crystals.Such a wide photonic bandgap may find application in controlling light,in wide stop band filtering,in solar energy utilization and in heat energy engineering.