Abstract: The decay pathways in successive decay chain were coded with binary digits. Based the coding approach and by using the E-factor method and recursion algorithm, a general purpose computer code DecayChain for calculation of the growth and decay of any member in a successive decay chain was written. The usage of decay chain code was demonstrated by the calculation of individual activities of each progenies and the total activity for the successive decay chain 228Th through 208Pb (9 members). When the relative detection efficiencies of chain members happen to meet an equation deduced in this paper the total counting rate will exponentially decrease with time with a single half-life. This conclusion was verified by the calculation performed with DecayChain for a 4-membered decay chain.