自己找到答案了。 Do I have to maintain a minimum income during the processing of the application?
Your Minimum Necessary Income must meet or exceed the Federal Income Table for Parents and Grandparents Sponsorship above on the date on which the sponsorship application is signed until the day your family members are permanent residents.
Income may be reassessed at any time during processing if new information indicates that you may no longer meet the minimum income requirements or if more than 12 months have passed between the dates on which we receive your application and when processing of the application begins.