The carboxylic acrylate raw rubber with low gel content and number- average molecular weight about 3.00 × 10⁵ was prepared through semi- continuous emulsion polymerization using ethyl acrylate and butyl acrylate as main monomers, methoxyethyl acrylate as functional monomer and isocyanate butyl acrylate as vulcanization monomer. In order to reduce the gel content caused by the attack of free radicals on α-H located on the copolymer backbones and the nucleation of hydrophilic monomers in the aqueous phase, the effects of polymerization conditions, the dosage of components and post-treatment conditions on the gel content and number-average molecular weight of the copolymer were studied in detail. Result show that the gel content could be decreased from 13.20% to 3.57% by controlling the polymerization temperature at 55 ℃ and adding 25% monomers during the first polymerization stage. Furthermore, the gel content could be continuously lowered to 0.10% if the n- dodecyl mercaptan is used as chain transfer agent and the dosage controlled at 0.025% , while potassium carbonate as pH conditioner at 0.40%, and n-heptane as solvent at 5.0%. In addition, some strategies, such as adding a small amount of sodium diethyldithiocarbamate to terminate the polymerization, using NaCl aqueous solution as flocculating agent to prevent chelation between carboxyl groups and multivalent metal ions, and drying the copolymer below 80 ℃, could be applied to reduce the gel content. Comparing with the same kinds of carboxylic acrylate raw rubber at home and abroad, the gel content in this study is lower, indicating the better products could be obtained from this kind of raw rubber.