Based on tunable semiconductor laser absorption spectroscopy (TDLAS) technology, a grid format laser channel is arranged at one or more cross-sections of the furnace to simultaneously measure gas concentrations and combustion temperature parameters such as O2, CO, H2O, and generate a three-dimensional analysis diagram of the furnace combustion conditions in real time. This solves the technical problem of parameter measurement in the boiler furnace, achieves accurate measurement of the combustion process, and provides a basis for boiler combustion optimization and economic operation. Also known as boiler CT.