Aiming at the shortcomings of the modified Anderson-Andreessen model（MAA model） in the mix design of ultra-high performance concrete（UHPC）， a physical and chemical based collaborative optimization method was proposed. Firstly， the multiple effects of the key parameters of MAA model， particle distribution modulus（q） and maximum aggregate size（D_max） on the performance of UHPC matrix are explored through experiments， and the optimal D_max and q value are found. According to the development trend of cement hydration degree， a new cement hydration spherical shell model is used to establish a new cement hydration equivalent particle size to optimize the MAA model.