The Uniform Customs and Practice for Documentary Credits (UCP), which used in the international trade, will be amended in 2006. Some argument issues based on the UCP500 and the practice of international trade will be adjusted significantly. This study focuses on the changes of regulations for letter of credit (L/C), which will be provided in UCP600, especially in the deferred payments and the applicability of Article 23. And then, the International Standby Practice 98 (ISP98) and the Electronic Presentation of eUCP were discussed in the light of guarantee and the security of electronic transaction. By the effective regulations and trade development, this article believes that the letter of credit will become one of the most secure instruments for trade financing.