Hfrhyu

I have two layer (A, B). I need copy polygon from layer A and replace polygon in layer B, but only geometry. I want to preserve original attribute table from layer A.

I would consider using the arcpy.da.UpdateCursor and SHAPE@ token for representing the geometry object. First, you have iterate through the rows to find if the value in some unique ID field matches, and if yes > replace the source geometry with the target one.

If you are only dealing with a few polygons, I would use the Replace Geometry tool on the Advanced Editing toolbar. See http://resources.arcgis.com/en/help/main/10.1/index.html#//01m80000001s000000

Alternately for a few polygons you could copy and paste the polygon(s) into layer B and then use the attribute transfer tool on the Spatial Adjustment toolbar to copy the attributes into the copied polygon; then delete the poly to be replaced.

But if you want to do this for all or many polygons and you have ArcInfo/Advanced, you could convert the affected layer B polygons to points inside the shape (and then later delete these polygons), convert the matching layer A polygons to lines, and then build polygons using the points as attributes. Check to make sure no point on the edge of one shape in B is not in the matching A. Add these new polygons to layer B. Use copies in case of mistake. My guess is Alex's answer is the most elegant, however.

As already mentioned you can use the da.UpdateCursor to update geometries. The geometries from A is stored in a Dictionary using the da.SearchCursor. The Dictionary is then used in the UpdateCursor to replace geometries where IDs match:

import arcpy

#Change to match your data:
arcpy.env.workspace = r'C:database.gdb'
A = 'featureclass1'
idfieldA = 'ID123'
B = 'featureclass2'
idfieldB = 'ID456'

#Build a dictionary with IDs as keys and geometries as value
geometries = key:value for (key,value) in arcpy.da.SearchCursor(A, [idfieldA, 'SHAPE@'])

#Empty list to store ids in B not found in A
notfound = []

#Update B with geometries from A where ID:s match
with arcpy.da.UpdateCursor(B, [idfieldB, 'SHAPE@']) as cursor:
 for row in cursor:
 try:
 row[1] = geometries[row[0]]
 cursor.updateRow(row)
 except:
 notfound.append(row[0])

print 'Found no id match and could not update geometry for IDs: ', notfound

As stated there is the Replace Geometry Tool. You can also use copy/paste and another doc about copy/paste between databases. If you are comfortable with programing, the arcpy.da.search and update cursor can also do the trick.