The invention provides N-full aromatic hydrocarbyl bisphenol-diamine tetrafunctional fluorene-based benzoxazine and a preparation method thereof. A new N-full aromatic hydrocarbyl bisphenol-diamine tetrafunctional benzoxazine monomer is obtained by the following steps: using trifluoroacetic anhydride to protect amino in 2, 7-dihydroxy-9, 9-bis-(4-amino phenyl) fluorene to produce 2, 7-dihydroxy-9, 9-bis-(4-trifluoroacetyl phenyl amino) fluorene, then performing Mannich condensation reaction of the 2, 7-dihydroxy-9, 9-bis-(4-trifluoroacetyl phenyl amino) fluorene and aliphatic amine and paraformaldehyde to produce a 9, 9-bis-(4-trifluoroacetyl phenyl amino) bisphenol fluorene-based benzoxazine monomer, then performing amino deprotection, and performing secondary Mannich condensation reaction with a phenolic compound and paraformaldehyde to finally obtain the new N-full aromatic hydrocarbyl bisphenol-diamine tetrafunctional benzoxazine monomer. The problems that fluorene-based benzoxazine with a structure with larger steric hindrance is small in molecular weight, low in crosslinking density, and poor in toughness and thermal performance reduction caused by the introduction of flexible groups can be solved, and the processing properties of polymers can be improved.