Hung Yen orange trees, a type of orange that come from “Vinh oranges”, which was cultivated in Hung Yen province, is one of the key fruit crops that is researched, planned and developed in priority by the government of Hung Yen province with purpose to become the brand name "Hung Yen oranges". Currently, the Hung Yen orange trees is cultivated in 8 of 10 districts/cities in the province grown most in Phu Cu district. Cultivation techniques of farmer (irrigation, fertilizing, etc.) for Hung Yen orange trees are mainly implemented by their experience then the productivity and quality of Hung Yen orange are affected. In the context reasonable irrigation with fertilizing process has been applied successfully in concentrated orange cultivation areas in the Northern Mountainous, North Central, Southeast regions… in Vietnam, the research on building a reasonable irrigation with fertilizing process for Hung Yen orange trees to solved mentioned above problems has very high practical significance. This paper presents the results of research on building a reasonable irrigation with fertilizing process for Hung Yen orange trees in its business period. The results show that with irrigation rates of 50¸60 (liters/tree/times) and 35¸40 times /year, using irrigation technique with fertilizing, orange productivity increases by at least 20%, reduction of fertilizer by 15%¸20%, saving labor and electricity costs... in comparation with traditional methods. The process has been approved by the Department of Science and Technology of Hung Yen province and is recommended for application for Hung Yen orange cultivation throughout the province.