Intrafibrillar　mineralized　collagen　is　the　main　form　of　natural　mineralized　collagen　in　bone　matrix.　However,　the　mechanism　involved　in　the　intrafibrillar　mineralization　is　still　unclear.　Here,　by　measuring　the　changes　of　Zeta　potential　and　adjusting　the　osmotic　pressure　of　collagen　fibers　to　study　the　mechanism　of　intrafibrillar　mineralization.　The　changes　in　zeta　potential　and　reduction　in　size　during　the　formation　of　amorphous　calcium　phosphate　(ACP)　after　adding　negatively　charged　polyacrylic　acid　(PAA)　and　positively　charged　cationicpolyacrylamide　(CPAM)　indicate　that　the　stabilization　mechanism　of　ACP　induced　by　polyelectrolyte　compound　is　charge　balance.　Then,　osmotic　pressure　pressures　charge　balancing　stabilized　ACP　into　collagen　fibers　to　induce　intrafibrillar　mineralization.　This　discovery　provides　basis　for　further　understanding　the　intrafibrillar　mineralization,　preparing　new　biomimetic　mineralized　materials　and　promoting　the　development　of　tissue　engineering.