Abstract: Using beta-2 adrenergic receptor, 5-hydroxytryptamine and angiotensin Ⅱtype 1 receptor as control, we here established a method for rapid prediction of the initial position amino acids of N-terminal, C-terminal, intracellular loops, extracellular loops and transmembrane (TM) regions in G protein-coupled receptors (GPCRs), and successfully predicted the structure of Mas-related G protein-coupled receptors X3 (MRGPRX3). To achieve this purpose, nanoluciferase (Nluc) was inserted into the different sites of these GPCRs′ sequence by sequence and ligation-independent cloning (SLIC) method, and the luminescence value were measured to distinguish the different parts of GPCRs. The results showed that luminescence values of NLuc luciferase at TM region were less than 100 000, and the values were higher than 1 000 000 at N terminal, C terminal, or extracellular loops and intracellular loops, and the values were between 100 000 and 500 000 at junction. The predicted MRGPRX3 structure was analyzed in detail and was compared with AlphaFold predicted structure. In conclusion, this method could provide useful information of GPCR structure model for the ligand virtual screening, and could provide certain experimental basis for structural pharmacology.