The invention discloses a gas turbine combustor adopting synthesis gas fuels and a control method for the gas turbine combustor. The gas turbine combustor is characterized in that multiple combustion nozzles on the top of the combustor are used for transferring air and fuels into a combustion chamber from top down; an outlet at the bottom of the combustor communicates with a turbine; separated air passages and fuel passages are integrated by the combustion nozzles; pressure or flow measuring devices are arranged on the combustion nozzle air passages for measuring the flows of air; external synthesis gases mixed with steam or other incombustible gases pass through the fuel passages; flow adjusting devices are arranged on the upstream of steam passages or other incombustible gas passages; and a control device controls the flow adjusting devices to adjust the flows of steam or other incombustible gases according to the air flow, the synthesis gas flow and the components of each combustion nozzle, so that the fuel flow and components, entering a combustion chamber, of each combustion nozzle are changed, and therefore the a proper ratio of the air flow passing through each combustion nozzle to a fuel value is reached. By adopting the gas turbine combustor disclosed by the invention, the synthesis gas fuels can be stably combusted in the gas turbine combustor; partial overheating of the combustion nozzles is avoided; and meanwhile, nitrogen oxide emission is reduced.