A novel design approach of realizing flattened mode large mode area photonic crystal fibers (PCFs) is presented by introducing a depressed-index region in the core of 7-rod core triangular PCFs. The influences from structural parameters,such as the size of depressed inner core,air hole pitch and the relative size of air hole,on the refractive index of inner core and the fundamental mode area are calculated with full-vectorial finite-difference method. A flattened mode PCF with mode area as large as 2000 μm2 is given,which can be easily fabricated with present technique. In the simulation,it is also found that less higher order modes will be contained in the fiber by scaling the depressed inner core and light wavelength as well as decreasing the relative size of air hole.