In this paper, propagation of quasi-continuous wave in photonic crystal fiber (PCF) is theoretically and experimentally investigated. With the nonlinear Schrdinger equation (NLSE) and split-step Fourier transform method, evolution of spectrum and pulse profile of quasi-continuous pump is numerically simulated, and the nonlinear mechanism for supercontinnum (SC) generation is analyzed. By comparing different simulative conditions, it′s shown that modulation instability (MI) in anomalous dispersion region dominates the spectrum broadening. Moreover, the effects of pump power, pulse width and fiber′s nonlinear coefficient on SC are also studied. Based on the theoretical results, quasi-continuous wave with pulse width of 80 ps was lunched into a 70m long nonlinear PCF and SC with the spectral range from 1300 nm to 1700 nm was generated, covering the whole communication window.