To reliably track stars and measure the transmittance of the whole-layer atmosphere at night, a two-dimensional direct-drive star-following turntable was developed using a direct-drive torque motor and a circular grating absolute encoder as servo parts. These parts offer the advantages for the turntable of high positioning accuracy, good environmental adaptability, and long-term field operation without maintenance. The turntable can realize the functions of the long-term tracking of target stars at night and automatic star change. Combined with the image acquisition system mounted on the turntable, which comprises a telescope, CCD camera, and filter wheel, the measurement experimental platform is built. The measurement experimental platform adopts the master-slave control mode. The upper computer controls the image acquisition system and provides the azimuth deviation feedback of the turntable to the lower computer. The control system of the tracking star turntable of the lower computer adopts the ARM7 digital processor loaded with the Linux system as the control core and a built-in self-developed star map. It realizes the complete function of the transmittance measurement of the whole-layer atmosphere by the collaboration of the upper and lower computer software developments. The turntable function verification experiment, the transmissivity measurement experiment of the whole-layer atmosphere, and contrast experiment using radar were conducted. Results show that the two-dimensional direct-drive star-following turntable can track the target star for a long time and automatically change the star for measurements at night. Moreover, the telescope system mounted on the turntable can reliably reverse the transmittance of the whole-layer atmosphere at night based on the image data of stars, meeting the functional requirements of measurement tests.