Abstract: How can we measure time? That is one of the basic concerns of mankind, and is closely related to people's daily life. With the development of science and technology, time measurement has become more and more accurate. In recent years, optical clocks have made great progress, and have become the world′ s most accurate time measurement tools. However, they are often bulky and can only work in the laboratory environment, which greatly limits their application. Scientists would like to have a portable, reliable, quasi-continuous running, and highprecision optical clock, but this is a challenging task. In this article, we will first briefly introduce the principle of optical clocks, then describe our recent research on a portable Ca⁺ optical clock, and finally discuss some possible improvements for the near future.