Abstract: The depletion calculation in reactor physics requires depletion chain data. However, the depletion chain that originates from evaluated nuclear data library is unnecessarily detailed for assembly and micro-depletion calculation, while conventional depletion chain compression methods are semi-empirical with limited application scope and accuracy. In this paper, a method that compresses depletion chain based on quantitative significance analysis of each nuclide and reaction channel is proposed. The significance analysis uses fine depletion chain computation results of representative problems as data source, and it is carried out by evaluating the influence on neutron absorption, production and number densities of target nuclides, induced by each basic unit compression. The method is applied to depletion chain compression in the context of PWR assembly calculation. Fine and compressed depletion chain computations of selected test cases are performed. The comparison among obtained numerical results show that, while preserving accuracy requirements, the proposed depletion chain compression method is capable of significantly reducing the complexity of the depletion chain, and the demanded storage and time savings are achieved consequently.