In this paper，abstraction and gel permeation chromatography (GPC) were used to deter-mine the monomer conversion in the crosslinking copolymerization of styrene with bismethyl acrylate bisphenol-A．It is indicated that A-MA possesses high copolymerizing reactive with styrene．Affected by heat of polymerization and viscosity of the system，the crosslinking copolymerization has obvious self-acceleration．In the self-acceleration，the temperature of the system is higher than the water bath temperature (58℃)，so the crosslinking copolymer-ization will reach high monomer conversion comparing to homopolymerization of styrene．The experimental results showed that because of the high copolymerization reactivity of A-MA，gel forms as soon as the reaction starts，but sol forms very little，before the monomer conver-sion rises to 40％．When sol forms 2.4% in the system，the monomer conversion win reach 63.1％，and the sol is continuously transfer to gel in the whole polymerization．This is oppo-site to the gelation in the condensing polymerization of multi-functional groups．Gel fraction of crosslinking copolymer is affected by the heat treatment at temperature above Tg．When A-MA is up to a certain content(A-MA>5.5×10-4)，the gel fraction win increase．At the same time，the amount of styrene will decrease after heat treatment；The sol fraction will de-crease when the concentration of A-MA is high(>5.5×10-4) and increase when the concen-tration of A-MA is low (-4)，because of the reaction of the double bond suspending in the system．The initial formed sol has very high MW．Through studying the GPC curves

it is found that the higher the monomer conversion is，the lower the MW of forming sol be-comes．This lead to the widening of MW distribution and the lowering of MW of whole sol in the sample．