The product delivery plan for ethylene plant in rundown case is usually considered at the beginning of design. Different rundown cases have diverse and significant impact on the refrigeration system. Rundown case is the critical case for the design and selection of refrigeration compressor. Taking a 1.0 Mt/a ethylene plant as an example, this paper compares the effects of two rundown cases on refrigeration system from the aspects of compressor power, utilities consumption, energy consumption and equipment investment. Setting rundown cases can ensure the continuous and stable operation of ethylene plant, but the energy consumption and equipment investment will increase accordingly. Multi-faceted analysis and comparison should be made during planning and decision-making.