Holding advantages including high accuracy, non-contact measurement, and full-filed measurement, single-wavelength digital holographic systems are generally used for the measurement of micro-scale objects with continuous morphology. Developed from dual-wavelength interferometry techniques, multi-wavelength digital holographic systems can measure objects with complex shapes and larger scales, which extends the application range of digital holographic metrology. In recent years, there are two main research topics in multi-wavelength digital holography area. First, many types of measurement methods and/or optical setup according to realistic requirements are proposed; in addition, enhancement are achieved in image processing techniques such as noise reduction algorithm, numerical reconstruction and phase aberration compensation to improve the computational efficiency and result accuracy.