This paper presents an optimized structure of photonic crystal fiber (PCF) by using genetic algorithms (GAs) and finite different frequency domain method. Our goal is to find a structure having small diffraction angle and good confine property. We also compare the optimal field profile with fitting Bessel function. Although the diffraction angle of Bessel functions is narrower than that in our case, the mode of the optimized structure provides a better confinement. The diffraction angle of optimal PCF can be decreased about 18.2% comparing to the non-optimized case.