The reaction system for TRAP makers of Common Carp (Cyprinus carpio),one of the major cultured fishes,was designed. The factors of reaction system including Mg²⁺ ,dNTPs,Taq DNA polymerase,DNA template and primer concentrations were optimized and a stable,repeatable TRAP-PCR system for Common Carp was established. The PCR was performed with a final volume of 15 μl reaction solution containing 1. 5 mmol /L of Mg²⁺ ,0. 35 mmol /L of dNTPs,3 mmol /L of each unlabeled 700- and 800- arbitrary primers,10 pmol /L of the fixed primer,60 ng of DNA template and 1. 0 U Taq DNA polymerase. The TRAP reaction program consisted of a pre-denaturing of template DNA at 94℃ for 4 min,followed by 5 cycles of denaturing at 94℃ for 45 s,annealing at 35℃ for 45 s,prolonging at 72℃ for 1min,35 cycles of denaturing at 94℃ for 45 s,annealing at 53℃ for 45 s,prolonging at 72℃ for 1min,and a final prolonging at 72℃ for 10min. This optimized TRAP- PCR reaction system provided a new molecular marker for the future study of genetic diversity,germplasm identification,genetic linkage map construction and relationship analysis in Common Carp.