Firstly,the qualitative relationship is verified by test data between Secondary Dendrite Arm Spacing(SDAS)and tensile strength(σb),and the quantitative equation is σb =641.75(SDAS)-0.28,deduced by linear regression method.Meanwhile,Furer-Wunderlin formula is equivalently transformed to SDAS = A* ×(Ts)1/3 by modifying constant part to A*.Then,the method is deeply studied to get SDAS rapidly and accurately,The first step is to obtain actual local solidification time(Ts)by calibrating solidification temperature by casting simulation and measurement.The second step is to calculate SDAS by modifiedtheoretical formula(SDAS = A* ×(Ts)1/3).The third step is to calibrate proper A* by SDAS test data.Finally,the research method is applied to the same kind of aluminum alloy cylinder head development,the head passed the reliability test once time and reduced test cost effectively and improved the quality significantly.One of the study results is that SDAS and tensile strength(σb)have quantitative relationship: σb = 641.75(SDAS)-0.28.SDAS sample is obtained easier than tensile strength specimen and break through the limitation of the tensile strength specimen from product.SDAScan be as an indicator to evaluate tensile strength in the early stage of product development.The other is that the method to get SDAS is innovative and feasible by combining withcast simulation and modified theoretical formula(SDAS = A* ×(Ts)1/3),but it is necessary to calibrate two key parameters of local solidification time Ts and A*,and the proper A* is range from 6.5 to 7.5 for aluminum alloy cylinder head.