Based on many-beam Schaeublin-Stadelmann diffraction equations and elasticity theories of defects, the transmission electron microscopy (TEM) diffraction contrast of dislocation loops within thin TEM foil is investigated systematically. Firstly, TEM diffraction contrast images of Frank dislocation loops in ion-irradiated copper are simulated with two-beam Howie-Whelan and many-beam Schaeublin-Stadelmann diffraction equations for verification; Then, the classic L-g-b relation of dislocation loop diffraction contrast is revisited, and effects of two-beam and many-beam diffraction conditions on the image contrast features are compared. Afterward, effects of anisotropic ratio on the black-white lobe features of dislocation loops are studied. Additionally, effects of loop depth within thin foil on the black-white lobes feature of dislocation loops are studied, and anisotropy will not change the flipping feature of the diffraction contrast lobes.