Liquefied natural gas (LNG) fuelled engines have been widely equipped on heavy duty vehicles both for fuel-economic and environmental protection concerns, however, they always suffer from deteriorated combustion performance and flame stability due to relatively low burning velocity of methane for lean mixture. In this paper, experimental study was conducted on a turbo-charged, spark-ignition, lean-burn LNG engine with methanol port injection. The combustion characteristics such as cylinder pressure traces, heat release rate (HRR), mass fraction burned (MFB), ignition delay, centroid of heat release, position of CA50 and CA90, as well as cyclic variation of peak pressure were analysed under light load (BMEP=0.3876MPa) with different methanol substitution rates (MSR=0%, 5.2%, 10.2%, 17.2%). The experimental results show that combustion phase advanced with increment of MSR due to faster burning velocity of methanol. Increase the MSR from 0% to 17.2%, the Centroid of heat release advanced from 8.59º ATDC to 6.46º ATDC, the position of CA50 shifted from 7.83º ATDC to 6º ATDC, the crank angle corresponding to maximum in-cylinder pressure (Pmax) moved from 11.32º ATDC to 9.65º ATDC. Shorter ignition delay and combustion duration, as well as higher cylinder pressure and maximum rate of pressure rise, were achieved compared with those in pure LNG mode under light load. The interdependence between pressure parameters and their corresponding crank angle becomes weaker with more MSP. The coefficient of variation (COV) of maximum in-cylinder pressure decreased slightly and the crank angle corresponding to Pmax scattered more around with the increment of MSP.