With the combination of mechanochemiluminescence from 1,2-dioxetane coupled polymers and granulated conjugated microporous polymer (CMP) nanosheets, a new kind of filling-type mechanolumninescent polymer composite was developed. Herein, polymeric 1,2-dioxetane performed as an autoluminescent probe of chain scission. Besides benefiting from their excellent optical properties and good interfacial compatibility with poly(methyl acrylate) (PMA) media, two stable and fluorescent CMP nanosheets were prepared and dispersed in crosslinked PMA, which can serve as effective energy acceptors and reinforcing nano-fillers. These polymer nanocomposites present both reinforced mechanical strength and mechanochemiluminescence, and offer exciting opportunities to study the failure process of polymer nanocomposites with unprecedented temporal and spatial resolution.