Disclosed are a method and a device for performing sidelink communication in a wireless communication system. Specifically, the method performed by a first terminal may comprise a step of transmitting a specific sidelink message including at least one piece of information among first information and second information to a second terminal, wherein: a transmission period of the first information is set to be longer than a transmission period of the second information; a first modulation order to be applied to the first information and a second modulation order of the second information are set differently from each other; and when the first information and the second information are concurrently transmitted through the specific sidelink message, modulation symbols of the first information and modulation symbols of the second information are mapped by considering a requirement noise ratio for each of the first modulation order and the second modulation order.