Tremendous burden is compelled on the energy consumption of data centers with the rapid development of information technology, and a healthy thermal environment is critical for improving the cooling efficiency of data centers. Furthermore, the thermal management of the data center is determined by the evaluation of its thermal environment. However, most of the existing evaluation metrics describe the thermal environment through a single scale, which cannot fully reflect the thermal performance of data centers at different scales. To simplify the evaluation of the thermal environment in data centers, a novel multiscale evaluation metric of the recirculation and hot spots index (RHSI) is proposed in this study. The numerical model of an operating data center is established and verified with the experiments on site. Then, the thermal environment of the data center is evaluated based on the RHSI and the existing metrics. Finally, the applicability of the RHSI is further discussed from different scales in detail. The results show that all bypass airflow, hot recirculation, and local hot spots can be derived from the proposed RHSI simultaneously by comparing with the evaluation metrics of supply heat index (SHI) and rack cooling indicator (RCI) at the room scale, β at the rack scale, and index of mixing (IOM) at the row scale. The proposed RHSI can provide a guiding significance for the thermal management of data centers.