Log is an important carrier of a computer system, which records the states of events, and a log system is responsible for log generation, collection, and output. OpenHarmony is a new open-source, distributed operating system for smart devices in all scenarios of a fully-connected world. Prior to the work described in this study, many key subsystems of OpenHarmony, including the log system, had not been built. The open-source feature of OpenHarmony enables third-party developers to contribute core codes. To solve the problem of the lack of a log system of OpenHarmony, this paper mainly does the following work: ① It analyzes the technical architecture, advantages, and disadvantages of today’s popular log systems. ② It clarifies the model specifications of the log system HiLog according to the interconnection feature of heterogeneous devices in OpenHarmony. ③ It designs and implements the first log system HiLog of OpenHarmony and contributes it to the OpenHarmony trunk. ④ It conducts comparative experiments on the key indicators of HiLog. The experimental data show that in terms of basic performance, the throughput of HiLog and Log is 1500 KB/s and 700 KB/s, respectively, which indicates that HiLog has a 114% improvement over the log system of Android. In terms of log persistence, the packet loss of HiLog is less than 6‰ with a compression rate of 3.5% for persistency, much lower than that of Log. In addition, HiLog also has some novel practical functions such as data protection and flow control.