Alar rock mass exposed in the Koktokay area of northern Xinjiang is composed of different types of intrusive units and has typical characteristics of complex granite basement. This study obtained LA-ICP-MS zircon U-Pb isotope ages of 217.3 ± 3.8 Ma, 218.6 ± 2.4 Ma, and 216.5 ± 6.3 Ma for medium to fine-grained biotite diorite granite, medium grained porphyritic diorite syenite granite, and medium coarse porphyritic diorite syenite granite, respectively, which are products of Late Triassic magmatic activity. The rocks are characterized by high silicon and low titanium, rich in potassium and aluminum, and poor in magnesium. The main body is the peraluminous potassium basalt series, with a differentiation index (DI) of 83.71-92.52 and an average value of 88.63, reflecting a high degree of magma crystallization differentiation; Strong negative europium anomaly (δ Eu=0.30-0.72) may be related to the fractional crystallization of plagioclase; Enriched with large ion lithophile elements Rb, Th, U and rare earth elements La, Ce, Nd, Sm, deficient in Ba, Nb, Sr, P, Ti, it belongs to a typical low Ba, Sr granite, indicating that the rock mass may be a product of low-level partial melting of crustal materials. The 176Hf/177Hf values of medium grained porphyritic biotite syenogranite and medium coarse-grained porphyritic biotite syenogranite are 0.282642-0.282800 and 0.282675-0.282763, respectively. The ε Hf (t) values range from -0.02 to+5.73 and+1.03 to+4.37, and the t DMC model ages are 759-1052 Ma and 827-993 Ma, respectively, indicating that the magma may have originated from partial melting of crustal materials from pre Cambrian microcontinents and the involvement of mantle derived materials. The rock body exhibits strong differentiation characteristics of I-type granite or A-type granite, with some exhibiting characteristics of S-type granite, indicating that the magma origin may not be a single source melting, or there may be a mixture of mantle derived magma and crustal material magma source areas, and magma evolution may involve both crystallization differentiation and assimilation mixing. Based on regional data, it is believed that the Alar complex granite was formed in an intraplate extensional environment, and its magma mainly comes from partial melting of crustal materials, with a small amount of mantle material possibly infiltrating into it. The heat source required for multi-source magma mixing in the lower crust may be related to the remote effects of the Siberian super mantle plume activity.