This　study　investigates　the　changes　of　tannic　acid　(TA)　at　varying　concentrations　in　cement　pore　solution.　Interestingly,　TA　spontaneously　forms　nanosheet　tannic　acid-calcium　polymeric　net-works　(TA-Ca)　by　interacting　with　Ca2+.　Spectral,　thermal,　ionic　and　organic　carbon　analyses　determine　the　composition　and　structural　characteristics　of　these　networks　and　detail　the　formation　mechanism.　The　networks　are　connected　via　hydrogen　bonding,　C-C　coupling　and　complexation.　Moreover,　network　composition,　structure　and　formation　are　closely　dependent　on　TA　concentration.　At　low　concentrations,　crystalline　coordination　polymer　networks　form,　following　second-order　kinetics　(key　factor:　Ca2+　concentration).　At　high　concentrations,　amorphous　C-C　coupled　polymer　networks　form,　following　first-order　kinetics　(key　factor:　catalytic　oxidation　of　Ca2+).　This　study　aims　to　elucidate　the　reaction　and　mechanism　of　TA　in　cement　paste,　providing　a　novel　theoretical　basis　for　applying　renewable　bio-admixtures　in　sustainable　construction.