Speech production requires control for coordination among different articulatory organs. During the natural speech, the articulatory co-variation is more common rather than compensation, but the studies supporting this view are few. In this study, the coordination of lip and tongue articulation was examined during speech using articulatory data. Native speakers of Chinese served as subjects. Speech materials consisted of short Chinese sentences, which include words having the cardinal vowels at different locations in sentences with and without emphasis. Articulatory movements were recorded using Microsoft Kinect for Windows and Terason T3000 ultrasound systems. After movement collection, 3D lip shapes were extracted from planar and depth images to examine the degree of lip deformation, and mid-sagittal tongue contours were tracked on ultrasound images to observe tongue surface deformation. The results indicate the tendency of co-variation between the lips and tongue rather than compensation, showing more extreme articulation of both for vowels at strong syllables than at weak syllables.