The analysis and calculation of the compensation for the phase mismatch of the f requency-doubling using the frequency space chirp introduced from prisms are mad e. The result shows that suitable lens can compensate the phase mismatch in a ce rtain extent resulting from wide femtosecond spectrum when the spectrum is space chirped. By means of this method, the experiment of second harmonic generatio n is carried out using a home-made femtosecond KLM Ti:sapphire laser and BBO cry stal. The conversion efficiency of SHG is 63%. The average output power of blue light is 320mW. The central wavelength is 420nm. The spectrum bandwidth is 5.5nm . It can sustain the pulse width of 33.6fs. The tuning range of blue light is 40 4-420nm，when the femtosecond Ti:sapphire optical pulse is tuned using the prism s in the cavity.