An audio device and a volume adjusting method are provided. The audio device includes a speed sensor, a first FIFO buffer unit, and a second FIFO buffer unit. The audio device generates audio signals by playing multimedia files and stores audio signals to the first FIFO buffer unit. The audio device collects ambient sound signals and stores collected sound signals to the second FIFO buffer unit. The audio device further analyzes stored audio signals and sound signals to determine a waveform of environmental noise signals, and determines a SPL of the environmental noise signals according to the determined waveform. The audio device then compares the determined SPL with a preset SPL and compares the sensed speed with a preset speed if the determined SPL is greater than the preset SPL, and adjusts the volume of audio signals according to a comparison result between the sensed speed and the preset speed.