Display omitted •Effects of gasifier conditions on the entire system performance are investigated.•The mass ratio of steam/coal has small effects on the overall thermal performance.•An optimal operation range exists for the mass ratio of O2/coal.•The carrier gas flow and the CO2 fraction in synthesis gas should be kept at a low level. The operating conditions of coal gasifier have significant effects on the overall system performance of an associated process. This study designs a methanol-electricity polygeneration system and presents a comprehensive discussion about the effects of the ratio of steam to coal, the ratio of O2 to coal, the ratio of carrier gas (CO2) to coal and the CO2 concentration in methanol synthesis gas on different performance indicators. The results show that the steam/coal ratio has slight effects on the overall system performance due to the offset in different sections. An optimal O2/coal ratio exists in the range of 0.84–0.86 to achieve the minimum unit water consumption and the maximum methanol production and energy efficiency, which is almost consistent with the range that the H2 concentration in gasifier syngas reaches the maximum value. The amount of carrier gas CO2 and the CO2 concentration in methanol synthesis gas should be kept at a low level to just meet the requirements of coal pressurization and synthesis reaction. This comprehensive sensitivity analysis can provide some significant guidance for the system design.