In this paper, chaotic light generated by semiconductor laser with optical feedback is employed as physical entropy source to generate high-speed random sequence. The relationship between autocorrelation coefficient of chaotic signal and run number of random sequence is analyzed. Based on the analysis, the changes of random sequence run number are further investigated at different ratios between laser relaxation oscillation frequency fr and random sequence generation rate fn. The results show that random sequence run can easily meet the requirement for run test of NIST SP800-22 when the ratio between fr and fn satisfies the equation of fr/fn=(2k+1)/4. When k in the equation is equal to 1, the maximal rate fn=4fr/3 of random sequence is obtained.