Abstract: Relevant market definition is one key step in merger review. Critical loss analysis is the popular relevant market definition method. The paper tries to generalize critical loss analysis by relaxing two assumptions, the demand curve is smooth and marginal cost is constant in the range of SSNIP, and proposes a new variant of critical loss analysis which is based on conjecture technology. In order to solve the invalidity of standard critical loss analysis when candidate market has a variety of differentiated products, the paper proposes a new way to implement critical loss analysis. The results show that: (1) statistic and constraint are both different between different versions of critical loss analysis, constraint is the same between different variants of critical loss analysis, but statistic is different between different variants of critical loss analysis; (2) when the demand curve has kinks or marginal costs is variable in the range of SSNIP, current critical loss analysis will define a too wide or too narrow relevant market; (3) when candidate market has a variety of differentiated products, the break-even version of critical loss analysis will be invalid. The paper proposes a new way to implement critical loss analysis which a valid and has strong operability. The paper has two purposes: one is helping parties concerned understand and use critical loss analysis properly; the other is improving Guidelines on Relevant Market Definition.