The first generation of femtosecond optical frequency comb (FOFC) based on the Ti:sapphire femtosecond laser in National Institute of Metrology of China, is improved and optimized in this paper. By changing the repetition rate of the femtosecond laser, the spectral broadening parts and the beat frequency signal detection, the complexity of spectral broadening is reduced and the stability of FOFC and the convenience for the frequency measurement are improved. With such an FOFC, the absolute frequencies of the I2-stabilized Nd:YAG 532 nm laser and I2-stabilized He-Ne 633 nm laser are measured. The experimenal results are in accordance with the recommended values by the International Committee for Weights and Measures.