One of the core issues for the A/B site doping in the bismuth layer magnetoelectric materials is to find out the evolution of the magnetic structure, crystal structure and elemental distribution, and the coupling effects between spin and lattice with the increase of ion substitution. Here, we have conducted systematic structural and physical property-studies on the series samples of Bi5Ti3Fei-xCoxO15. This work presents that Bi5Ti3Fei-xCoxO15 forms-a single four layer perovskite-like structure for 0 < x < 0.6, while a three layer perovskite-like structure block begins to arise for x > 0.67. With different cobalt content, the sample demonstrates antiferromagnetisin, spin state determined magnetism, or magnetic anisotropy determined magnetism. The weak ferromagnetism is considered to be induced by the larger displacement of Co3+ ions from the center of octahedra and the change of the spin state of Co3+ ions. It is also observed that Fe and Co elements are homogeneously substituted in the three layer structure block, accompanied by the rotation (and/or distortion) of BO6 octahedra.