Lithium is emerging as a key strategic mineral in China. The Jiajika deposit in the eastern margin of the Qinghai- Tibet Plateau is the largest hard- rock type lithium deposit in the world, and is accompanied by a large amount of beryllium, niobium, tantalum, rubidium, cesium and other rare metals. The morphology of unexposed granite bodies, the relationship between granite and pegmatite, and the spatial distribution of pegmatite and fine crystalline lithium deposits are the key points to understand the ore- controlling effect of lithium mineralization. In this paper, a three- dimensional model of the concealed granite dome is established by using high- precision gravity survey, and the morphology and extension of the granite body are deduced. At the same time, magnetotelluric sounding and drilling verification have also been used to reveal the relationship between the ultra- large and large lithium veins such as X03, 309 and 134 and the two- mica granite. On this basis, the understanding of the compound (polycentric) granite magma diapir dome, immiscible Li- F granitic magma pulsating filling and metasomatism, and semi- open shear- tension fractures controlling large veins are proposed. The phenomena that the fine crystalline lithium deposits dominate the ore field and coexist with pegmatite lithium deposits are discussed. This study is of great significance for the prospecting of the Jiajika area with high Quaternary coverage. The periphery of the polycentric small dome developed on the concealed granite stocks (branches) is a favorable position for prospecting, especially in the middle- south section of the dome near the Majingzi pluton. The inference that the concealed granite is leaning NNW needs to be verified in the northern part of the ore field. The deep extension of the granite body, the rock combination, and whether there is only a single rock type of two- mica granite, etc., and the abnormal enrichment process of rare metals and other issues still need to be investigated in order to make a breakthrough in lithium ore prospecting.