The invention discloses benzothiophene alkanol piperazine derivatives and their use as antidepressants. The invention discloses the said benzothiophene alkanol piperazine derivative having triple inhibition effect on the reuptake of 5-HT, NA and DA. Compared with clinical used antidepressants so far having single target, e.g. desipramine and fluoxetine, and clinical used antidepressants so far having double targets, e.g venlafaxine and duloxetine, the said benzothiophene alkanol piperazine derivatives of the present invention may have a broader indication range and less toxic and side effects to nervous system. The benzothiophene alkanol piperazine derivatives are the compounds with the following formula or their pharmaceutically acceptable salts, wherein Ar1, R1-R4, X, Y, m and n have the same definition as defined in claim 1.