Abstract: On a modified a six-cylinder heavy-duty diesel engine, the ethanol/diesel Reactivity Controlled Compression Ignition (RCCI) experiment was carried out to study the effects of premixing ratio on the chemical composition of ethanol/diesel RCCI exhaust particulate matter. The results show that the elemental composition of RCCI particles mainly includes C, O, Si elements, and trace metal Zr is also detected; with the increase of Rp, the elements of C and O in the RCCI particles increase, and the elements of Si and Cu decrease, and the element of Zr decreases to disappear. The research will deepen the understanding of RCCI particulate matter chemical composition's generation theory and provide technical support for reducing RCCI particulate matter emissions.