As the semiconductor industry develops and the device performance improves continuously, the feature size of semiconductor devices is becoming smaller and smaller, and the device structure is becoming more and more complex. Therefore, it urgently demands for the high performance of metrological instruments. This paper first introduces the measurement principle and the setup of through-focus scanning optical microscope (TSOM) method. This method can realize the nondestructive measurement of 3D geometric parameters, and has the advantages of high precision, fast speed, low cost, etc. It can meet the requirements of online applications. Then the paper introduces the research progress of TSOM method from two aspects: the construction of TSOM image and the extraction of structural parameters. Finally, it prospects the future research focus and development direction of TSOM method. This method is hopefully a new metrology method for China's semiconductor manufacturing industry, and provide important technical support for optimizing and upgrading China's semiconductor manufacturing process.