Based on the extended international arbitrage pricing theory (IAPT),an international multiple factors model is established.Through relative mathematical analysis,the behavior of international portfolio arbitrage is defined,and the trigger conditions and determinants are described by the numbers.The mechanism of the international portfolio arbitrage behavior is revealed as: through establishing portfolio to increase relativity of the assets,the assets used for arbitrage can be matched.Under the condition without any transaction cost,an optimal weight of portfolio arbitrage can be solved with the meanvariance method.