We introduce an experimental setup for the simultaneous measurement of axial and radial strain variations of a hybrid carbon nanotube (CNT) yarn actuator, where a paraffin wax is melt-infiltrated inside the CNT yarn. Such a hybrid yarn system has been known as a Joule-heating-driven tensile/torsional actuator due to a large volume expansion of the infiltrated paraffin upon a solid-to-liquid phase transition. During the operation of this actuator, however, the axial strain variations along the yarn axis and the diameter change of the yarn, which is the radial strain variations perpendicular to the yarn axis, had been measured separately, which prohibits the exact understanding of the whole actuation dynamics. In the new experimental configuration, a laser scan micrometer is employed for the in situ yarn's diameter measurement and is combined with the conventional tensile actuation measurement setup for real-time data-taking during the actuation. When the hybrid CNT yarn was tested, the synchronized strain variation data in the axial and radial directions were obtained, which helps the analysis of these actuation phenomena especially in the intermediate states.