North Vietnam Block is situated in Yunnan—Guangxi boundary, China, and northern Vietnam, is a key area for studying the interactions between Yangtze, Cathaysia and Indochina blocks. We investigated the contact relationships between “Xinzhai Formationcomplex” and metamorphic granitic rocks located in north margin of North Vietnam Block. We suggest that the contact relationships should be three new relationships (sedimentary contact, intrusive contact, transitional contact), instead of prior detachment fault contact. The sedimentary contact indicates the Sinian— Cambrian overlap (Southwest toward northeast) in north margin of North Vietnam Block. Intrusive contact and transitional contact reflect the emplacement of Caledonian granites in this area, which result in the forming of Dulong—Song Chay dome. The prior “Xinzhai Formationcomplex” includes Late Sinian — Cambrian System. The prior Palaeoproterozoic granitic gneisses should be Silurian tectonic—magmatic thermal event. The previous Silurian granites should be redivided into Neoproterozoic and Silurian granites.