The combustion characteristics of aluminum and boron nanoparticles were studied based on the optical diagnostics using a color digital camera and subsequent image processing and their morphologic features, temperature characteristics and the ignition time were obtained. In the experiments, the multi-diffusion flat flame burner (i.e. Hencken burner) was used to support a tunable high temperature ambience. A series of processes including dissolving the nanoparticles into the ethanol, ultrasonically dispersing, atomization, and diffusion-drying were used to generate well-dispersed nanoparticle aerosol. The flame images of the nanoparticles were recorded by a color digital camera under different experimental conditions. The signals of red, green and blue channels were derived from the color images to obtain the radiation intensity and the information of particle temperatures based on the Planck's law. The results indicate different particle temperature profiles at different ambient temperature. At a high temperature, the particle temperatures of Al and B decrease directly after ignition. At a low temperature, the particle temperature of Al increases slowly to a peak and then decreases due to the polymorphic phase transition of the alumina shell, while the particle temperature of B is nearly constant. The ignition process of B is divided into ignition delay and ignition stage, and the time could be defined from the flame images. The time of ignition delay for B ranges from 1.17 ms to 2.98 ms and the ignition time ranges from 0.31 ms to 0.85 ms.