Alzheimer's disease (AD) is one of the most devastating neurodegenerative diseases without effective therapies. Immunotherapies using antibodies to lower assembled Aβ provide a promising approach and have been widely studied. Anti-amyloid antibodies are often selective to amyloid conformation, and the lack of amyloid-antibody structural information limits our understanding of these antibodies' conformation selection. Gantenerumab and crenezumab are two anti-Aβ antibodies that bind multiple forms of Aβ with different Aβ epitope preferences. Here, using molecular dynamic (MD) simulations, we study the binding of these two antibodies to the Aβ fibril, whose conformation is derived from an AD patient's brain tissue. We find that gantenerumab recognizes the Aβ monomer fragment only at slightly lower pH than the physiological environment where His6 of Aβ is protonated. Both gantenerumab and crenezumab bind with integrated Aβ fibril rather than binding to monomers within the fibril. Gantenerumab preferentially binds to the N-terminal region of the Aβ fibril, and the binding is driven by aromatic interactions. Crenezumab can recognize the N-terminal region, as well as the cross-section of the Aβ fibril, indicating its multiple binding modes in Aβ fibril recognition. These results demonstrate conformation-dependent interactions of antibody-amyloid recognition.