Benzoyl peroxide (BPO)/N,N-dimethylaniline (DMA) redox system was employed to initiate the free radical polymerization of methyl methacrylate (MMA) resulting an oligomer, OMMA. OMMA was subsequently used as macromolecular reducing agent with BPO to initiate the polymerization of MMA, thus achieving poly (methyl methacylate) (PMMA). The initiation mechanism of BPO/DMA redox system, the polymerization behavior and the structures of the polymers were studied through gas chromatography (GC), NMR and triple-detection size exclusion chromatography (TD-SEC). Results show that the fragments from DMA and BPO in the obtained polymers are not equivalent, and the fragment from DMA is more than that from BPO, implying the existing of unknown reactions besides the initiation for benzoyloxy radical. The resulting OMMA (Mn≈2400, PDI=1.23), containing DMA fragments formed during the early stages, could be used as macromolecular reducing agent with BPO to form a redox system, acquiring PMMA exhibits high molecular weight (Mn≈3700) and broad molecular weight distribution (PDI=2.48).