Requirements for the effective real-time analysis of instant data modification of database systems have driven the rapid development of Hybrid Transactional/Analytical Processing (HTAP) database systems, which support to process both OLTP and OLAP workloads. To realize fair comparisons and healthy development, it is crucial to define and implement new benchmarks to evaluate new features of HTAP database systems. Firstly, this study analyzes the key characteristics of HTAP database systems and summarizes the distinct technologies in their implementations. Secondly, the difficulties of designing HTAP database systems and the challenges of constructing HTAP benchmarks are extracted. Based on these, the design dimensions of HTAP benchmarks are proposed, including data generation, workload generation, evaluation metrics, and consistency model supportability. This study compares differences between existing HTAP benchmarks in terms of design dimensions and implementation technologies and sums up their merits and defects in different dimensions. Additionally, the published benchmarks are demonstrated and their abilities of evaluating key features and supporting horizontal comparisons among HTAP database systems are analyzed. Finally, this study concludes the requirements for HTAP benchmarks and some future research directions, pointing out that semantically consistent workload control and fresh data access metrics are the key issue in defining benchmarks for HTAP database systems.