Evolutions of ultrashort pulse in time and frequency domain are modeled based on the nonlinear schrödinger equation by predictor-corrector split-step flourier method when the pulse travels in an all normal dispersion photonic crystal fiber. And the influences of the pulse duration and energy on generated continuum are also investigated. It is shown that a single pulse is maintained in the time domain and that a larger spectrum broadening is achieved with higher peak power. When the fiber is pumped by an unchirped Gaussian pulse centred at 1060 nm with duration about 50 fs and energy 1.5 nJ, good continuum is available after only 12 cm traveling distance with fine continuity and coherence. And a perfect continuum is achieved with duration about 15 fs and spectrum about 700 nm after pulse compression by a pair of prisms.