To overcome the deficiency of mean field method in introducing the intramolecular cyclization and the steric effects, the reactive bond fluctuation model was applied to study nonideal hyperbranched A(2) + B-3 polycondensation, which has high sensitivity of gelation to the concentration of monomers, the feed ratio and the reactivity of functional groups. Simulation demonstrated that the mean field theory overestimated hyperbranched polymerization especially at high reaction conversion in the system with low monomer concentration where the intramolecular cyclization and the steric hindrance play crucial influences on molecular weight, molecular weight distribution and gel point (GP). The dependences of GP on the monomer concentration, feed ratio, and the reactivity of groups are clearly shown. We further simulated a specific polycondensation system with aromatic terephthaloyl chloride (TCl, A2) and 1,1,1-tris(4-trimethylsiloxyphenyl) ethane (TMS-THPE, B3) (Macromolecules 2007, 40, 6846) using fitting technology, and estimated molecular weight, molecular weight distribution, GPs, and the conformation of hyperbanched polymer. It provides a feasible way to quantitatively understand hyperbranched polymerization with the reaction specificity. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5072-5082, 2010