The invention provides a method and apparatus for adjusting the definition of a video adaptively, a terminal device, and a storage medium, where a definition parameter of the video is dynamically adjusted adaptively according to a terminal parameter influencing the quality of a video call so as to ensure the video call in normal operation, and also better fluidity thereof. The method includes: detecting a terminal parameter influencing a quality of a video call, in a terminal device participating in the video call; and adjusting a definition parameter of the video upon determining that the terminal parameter satisfies a preset condition; wherein the definition parameter of the video includes any one or combination of a resolution, a bit rate, and a frame rate of the video.