This paper provides a comprehensive review of the field of multi-task assignment for multi-UAV, and outlines the typical techniques for task allocation in drone swarm missions, summarizing their respective advantages and disadvantages in two phases. Firstly, it describes the research background and significance of multi-UAV multi-task assignment problems, and briefly summarizes the basic characteristics of the task pre-allocation and task reallocation stages, and analyzes key issues at different stages. It then introduces two main categories of methods for UAV task assignment: centralized and distributed, and analyzes their applicability in the context of multi-UAV multi-task assignment at different stages. Finally, it gives suggestions on the key research directions of multi-UAV task assignment. This paper offers new research ideas and approaches to improve the quality and speed of solving task allocation problems in drone swarm missions, thereby providing important reference significance for a comprehensive understanding of drone swarm task allocation technology.