A compact high power supercontinuum source is designed and explored. A 1.5 m Yb-doped double cladding large-mode area photonic crystal fiber is employed as gain media of the laser. 0° end face of the fiber serves as a cavity mirror and output coupler. Stable mode-locking is obtained by using a semiconductor saturable absorber as another cavity mirror. A pair of grating is used for intra-cavity dispersion compensation. As a pump source, the laser generates 1.5 W, 494 fs pulses at 55 MHz repetition rate. Systemic study of the dynamics in the laser cavity is presented. Mode locking mechanism of the laser is demonstrated. Over an octave (680～1450 nm) ultra-flat supercontinuum with an average power of 500 mW is generated in a 1 m photonic crystal fiber.