The self-reference technique is widely used to measure the carrier-envelope phase offset (CEO) of femtosecond laser pulses in the normal femtosecond laser frequency comb system. However, the instability of the frequency comb system is increased because the photonic crystal fiber is introduced into the system to broaden the spectrum of femtosecond laser pulses outside the cavity. In this paper, we presented another method to measure specifically the CEO for the broad spectrum Ti:sapphire oscillator with the pulse duration of 7fs, namely the difference frequency technique, with which we have obtained the beat frequency signal with a S/N ratio greater than 31dB. This provided a good precondition for the next generation of the femtosecond laser frequency comb system without the photonic crystal fiber.