Abstract: The influences of trace elements Cu,Fe,Cr on high speed Zn-Ni alloy electroplating and their mechanism have been investigated.The Cu²⁺ in Zn-Ni electrolyte can easily deposit,but it is a harmful element;while Fe²⁺ and Cr³⁺ are difficult to deposit.The Fe and Cr in deposit can increase the corrosion resistance of Zn-Ni deposit.The electrodepositing mechanism of trace elements has been discussed,and the quantitative predication method for wheather trace element can deposit from electrolyte has been established.