An unified model is presented to establish the quantitative relations between yield strengths of aged Al alloys containing plate/disc like or rod/needle like precipitates and the sizes, volume percentages of precipitates, The nucleation, growth and coarse of the precipitates are integrated into the age strengthening model based on some acceptable assumptions. The aging strengthening of AA6061 and an Al Zn Mg alloy has been satisfactorily simulated and predicted. Furthermore, the dependence of aspect ratio of plate/disc like or rod/needle like precipitates on aging temperature and processing condition is discussed in detail.