Triaxial repeated load permanent deformation tests of two asphalt mixtures were conducted to investigate the flow characteristics of asphalt mixture under high temperature and heavy load. Then, a continuous function between permanent strains versus loading cycles was derived, and flow number was calculated by some algebraic manipulations of the second derivative of the proposed function. It is indicated that permanent strain increase with test temperature and stress, and permanent strain of mixture with larger maximum nominal aggregate size is smaller. The proposed function can well describe the whole three stages of permanent deformation for asphalt mixture. The calculated flow number is also different with mixture gradations and decreases with the stress and temperature. But the decrease range becomes smaller at higher stress levels and temperatures, especially at the extreme condition, and the difference among asphalt mixtures is inconspicuous. At this moment, permanent deformation resistance of different mixtures could not be distinguished by the flow number.
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