The combustion and emission characteristics of a dual fuel diesel engine with high premixed ratio of methanol (PRm) were investigated. Experiments were performed on a 6-cylinder turbocharged, intercooling diesel engine. Methanol was injected through the intake port and ignited by direct injected diesel in the cylinder, the maximum PRm was over 70%. The experimental results showed that with high PRm, the maximum in-cylinder pressure increased from medium to high engine load but varied little or even decreased at low engine speed and load. High PRm prolonged the ignition delay but shortened the combustion duration and decreased the in-cylinder gas temperature at ignition timing. Hydrocarbons (HC), carbon monoxide (CO), formaldehyde emissions and the proportion of nitrogen dioxide (NO2) in nitrogen oxides (NOX) increased significantly with the increase of PRm while NOX and dry soot emissions were significantly reduced, which meant the trade-off relationship between NOX and soot emissions disappeared. The increased HC, CO and formaldehyde emissions could be effectively reduced by diesel oxidation catalyst (DOC) when the exhaust gas temperature reached the light off temperature of the DOC. After DOC, the NO2 proportion in NOX was greatly reduced to less than that of baseline engine at methanol premixed mode but increased slightly at pure diesel mode. The maximum PRm was confined by in-cylinder pressure at high engine speed and load. But at low engine speed and load, it was confined by the high emissions of HC, CO and formaldehyde even after DOC. (C) 2014 Elsevier Ltd. All rights reserved.