Atom transfer radical polymerization（ATRP），reversible addition-fragmentation chain transfer（RAFT）and conventional free radical polymerization（FRP）of polyethylene glycol methyl ether methacrylate（PEGMEMA）and polyethylene glycol dimethacrylates（PEGDMA）were conducted respectively，and their reaction kinetics and gelation behavior were investigated with respect to the polymerization rate，vinyl conversion，gel point，and evolution of network. All the three systems experienced autoacceleration of the reaction. The rate autoacceleration in the ATRP was caused by diffusion-controlled radical deactivation，while that in the RAFT was attributed to diffusion-controlled addition of propagating radicals to RAFT-capped chains. In the ATRP and RAFT systems，the slow growth of primary chains allowed adequate chain relaxation and diffusion of reacting species，which reduced the probability of intramolecular cyclizations and limited the formation of microgels，leading to earlier gelation，as compared with the FRP system. The crosslinking networks in the ATRP and RAFT developed mainly through gel radical propagation with monomers，along with incorporation of branched polymers，resulting in a gradual increase in gel fraction and network density.