The content of calcium in milk is very important for the quality of milk as it can provide an important source of nutrition for the human body. It is of great significance to quickly determine calcium in milk. In this work, picosecond laser ablation spectroscopy was used to achieve quantitative analysis of calcium elements in milk with the emission spectral lines selection and calibration curves of calcium in milk. The linear fitting coefficient was more than 0.99, showing a good fitting effect. At the same time, the measurement setup was built on a breadboard, which could achieve portable, online, and rapid detection. The calcium element in random milk was detected by this technology, and the detection error was controlled below 2%, which verified the accuracy of the detection. This work realizes the real-time and online rapid detection of calcium in milks with different calcium content, which shows positive significance for the online quality inspection of products and the rapid analysis of calcium concentration.