Using laser-induced breakdown spectroscopy (LIBS), the main elements in fly ash, including C, Si, Al, Mg and Fe, are measured. KBr is employed as binder to press the fly ash powder to pellets. The differences of fly ash plasma characteristics in different gas environments (CO2, air, N2, Ar ) are analyzed, and their effects to unburned carbon measurements are studied. The results show that the spectral intensities obtained in argon are the highest among the four environments, and intensities in nitrogen take the second place. The intensities in air atmosphere are just a little less than those in nitrogen, while those in carbon dioxide are the least. Furthermore, carbon element in CO2 disturbs the unburned carbon analysis extremely. Comparing the plasma temperatures in different environments, plasma in CO2 atmosphere get the lowest temperature, implying it is the hardest to induce in CO2.