Due to the exhaustion of IPv4 address resources, the transition from IPv4 to IPv6 is inevitable and fairly urgent. Numerous transition mechanisms have been proposed to solve challenging issues of IPv6 transition. An inter-connection between IPv4 and IPv6 networks or hosts requirement has been happening throughout the IPv6 transition process. And one-time translation scheme is indispensable to achieve the inter-connection. In addition, double translation can be used in the IPv4-IPv6-IPv4 scenario. As a long-term strategy, translation scheme is important and inevitable. However, because of the diverse characteristics and transition requirements of practical networks and the lack of applicability analysis, the selection and deployment of transition mechanisms are facing with grand challenges. Targeting at those challenges, this paper investigates the basic issues and key elements of IPv6 translation transition mechanisms, and presents its first applicability index system. In particular, we analyze the applicability of existing proposed translation techniques based on the presented index system, which has significant guidance in the practical deployment of IPv6 transition techniques.