The invention provides pyrrolidine compounds, salts thereof, applications of the compounds or the salts thereof in nuclear magnetic probes and medicines, a reagent, and a medicine. The benzamide methylpyrrolidine compounds have a chemical structure represented by general formula (I); and in the formula (I), R<1> is selected from a methyl group, an ethyl group, a methoxy group, an ethoxy group and halogen, R<2> is selected from a methyl group, an ethyl group, a methoxy group, an ethoxy group and halogen, R<3> is selected from C1-5 alkyl groups and H, X<1> is selected from C1-10 alkylene groups or is deleted, X<2> is selected from -(CH2CH2O)n- (n is 1-5) or is deleted, X<3> is selected from C1-5 alkyl groups, X<4> is selected from oxygen, sulfur and a methylene group, and Ln is selected from Gd and Eu. The compounds have a gadolinium and europium chelating structure formed by combining with a dopamine D2 receptor and depending on intramolecular chelating groups, and specifically enhance the contrast of dopamine D2 receptor expression tissues on images in magnetic resonance imaging.