Applying to high performance concrete mix design, overall calculation method can fully quantify the various components of concrete. While the application of overall calculation is very wide, its applicability has weaken with the increase of fly ash. In particular, overall calculation is not applied to high volume fly ash concrete. The reason is simplely considered fly ash cement as a simple alternative to cement when designing of concrete mix, and then following the water-cement ratio strength formula to design concrete mix, neglecting the differences of contribution to concrete strength between fly ash and cement. To solve these problems, this paper considers the fly ash as a separate component of concrete, and re-establishes two variables strength formula based on water-cement ratio and fly ash dosage. On the basis of the generally applicable volume model of concrete, overall calculation is re-derived, then used to directly design high performance concrete mix ratio. Improved overall calculation method is more widely ,more scientific and more reasonable, and will have a far-reaching influence on the application of high volume fly ash high performance concrete.