Abstract: In order to analyze the phase matching of extreme ultraviolet high harmonics in the process of attosecond pulses generation,the analytic expressions were achieved based on the three-step analysis model for optical field ionization high-harmonic generation(HHG),and the harmonic spectral phase in the process of attosecond pulse generation was analyzed.It was found that,except the highest order harmonic,the spectral phase contribution of each harmonic consists of two sources of long trajectory electrons and short ones,and that,unlike the generated harmonics by the former,the spectral phase of those harmonics from the latter has regular phase relation among each other.The final conclusion is drawn that suppressing the long trajectory electrons can reduce the pulse width of attosecond pulses,which is of great significance to the issue of high harmonic phase matching in generation of attosecond pulses.