A method for mapping a low-dynamic range (LDR) video into a high-dynamic range (HDR) video and a device therefor are provided. The method includes a modeling process, and a mapping process. The modeling process includes training according to LDR videos of at least three different exposure levels to obtain a highlight reconstruction model and an exposure generation model, and the mapping process includes mapping an LDR video to be processed into an HDR video through the highlight reconstruction model and the exposure generation model. Accordingly, solutions to the problems of a multi-exposure synthetic image being too dark or too light is provided, and jitter in video synthesis, are provided.