Terahertz thickness measurement is very important in materials research and industrial test. And it can beused to measure various materials such as wood, paper, ceramics, plastics, and composite materials. Atomic superheterodyne terahertz detector has extremely high sensitivity. The sensitivity of terahertz electric field strength measurement can reach 5.76 μV/(cm·Hz^1/2). Simultaneously, the linear dynamic range is better than 60 dB. So, it can be used to precisely measure the thickness of materials through the terahertz transmission efficiency. The experiments in this work demonstrate the thickness measurement of sapphire crystal and organic materials PTFE. The terahertz signal is shown in Fig. (a) sapphire material and Fig. (b) PTFE material. The thickness can be calculated from the transmittance, and the result is consistent with the result measured directly with a vernier caliper. Furthermore, single-layer graphene and few-layer graphene can be clearly distinguished from terahertz transmission signals as shown in Fig. (c) graphene material. Even for niobium meta thin films with thickness of 1 μm, very weak terahertz signal can be well distinguished due to the high sensitivity of atomic superheterodyne terahertz detector. In summary, the technology developed for terahertz thickness measurement based on atomic superheterodyne detection is very important for detecting defects, checking coating, and measuring the parameters of materials.