A method for adjusting 3D video images is provided. The method includes the steps of : receiving a 3D video, wherein the 3D video includes a plurality of frames, and each frame includes a plurality of image blocks; obtaining a binocular parallax value between a left eye image and a right eye image which related to each other in the 3D video; calculating displacement of each image block based on the locations of the same image block in the different frames and calculating the image complexity of the 3D video based on the displacements of the image blocks of the frames; converting the 3D video into a 2D video and displaying the 2D video when the image complexity is greater than a predetermined value, and adjusting the definition of depth of each image block in each frame of the 2D video, and displaying the 3D video when the image complexity is lower than the predetermined value, and adjusting the binocular parallax of each image block of each frame of the 3D video according the image complexity of the 3D video.