Document.OMathJc (Word)

Returns or sets a WdOMathJc constant that represents the default justification—left, right, centered, or centered as a group—of a group of equations. Possible return values are wdOMathJcCenter - Center, wdOMathJcCenterGroup - Center as a group, wdOMathJcInline - Inline, wdOMathJcLeft - Left, wdOMathJcRight - Right.

ActiveDocument.OMathJc = wdOMathJcCenter