1,2,3,4-Tetrahydroisoquinoline derivatives and their synthesis method and application, the invention belongs to the technical field of drug synthesis, and relates to the general formula (I): X=(CH2)n, n=1-15 Or X=CO(CH2)n-1, n=1-15; R1, R2, R3, R4, R5, R6 are 1,2,3,4-tetrahydroisoquinoline compounds and their salts with different substituents , its preparation method and application in medicine. The invention discloses the chemical structure, synthesis method and in vitro acetylcholinesterase inhibitory activity of these compounds, which can be further developed as novel drugs for treating Alzheimer's disease.