To solve the problems of low production efficiency and poor quality consistency in the assembly of laser target designation (ALTD), a digital and smart assembly method of laser target designation based on digital twin was proposed. Through real-time data collection of automatic assembly machines and digital test instruments, we can dynamically optimize the assembly process and debugging parameters, and control the output quality of each process. We can simulate in virtual space by physical data and control physical space by virtual entity to achieve virtual-reality integration digital and smart assembly. In this paper, we expound the digital and smart assembly of laser rod components to show that the digital twin of ALTD can realize the resource optimization, process optimization, quality control, cost reduction and efficiency improvement in the assembly workshop.