Previousmonth syntax not working

Hi  Lijun_ , 

According to your description and the dax formula you provided, here is the test I did with my own sample, and there was no problem.
Since I don’t know the specific situation of your data, in order to help you better locate and solve these problems, I will attach my .pbix file to you. Please try to open it after you receive the file, and compare it with your data and file, to see if you can find any differences.

My Sample:

Result is as below.

Best Regards,

Yulia Yan

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