Hai Ngoai Ky Su is the notes written by the Chinese Buddhist monk Thich Dai San during his trip to Cochinchina (Central Vietnam) in 1695. This work was translated into Vietnamese in 1963 and was utilized by many researchers of the East Sea history as some parts in the notes is related to the name of Van Ly Truong Sa, or Paracel lslands of Vietnam. Due to some errors which have not been adjusted in the translation yet, there are several cases of mistaken citation from the translation in the thesis or research works of some authors in the country. In this article, the author compares the Vietnamese translation with the original text, revises the itinerary of Thich Dai San, analyzes some errors in the original and revises the errors in Vietnamese translation related to the place name of "Van Ly Truong Sa". Simultaneously, the article also briefly introduces the viewpoint of a number of some Chinese and Vietnamese researchers on the historical value of Hai Ngoai Ky Su in demonstrating the sovereignty of Vietnam over Paracel and Spratly islands.