I changed a different size monitor , the pics cannot be recognized

the captured pictures have to be the same pixel-by-pixel on both systems. So what counts is resolution and not screen size. In many situations (especially laptop widescreen and standard ration desktop monitor) you have interpolated pixels, that make that pictures look similar or identical, but on the pixel level they are different.

To test your situation, capture an object on both screens an have a look at them magnified, so you can compare the pixels visually.

Currently Sikuli has no feature to manage this situation, so you have to take 2 different image sets.

Verify your PPI (DPI) settings are the same on both systems. Also focus on capturing unique geometric primitives, especially as a test between both systems

If these are windows systems the following .vbs script will return in a message box the current PPI setting,this will spare a continual menu safari to get PPI settings on test systems

Const HKEY_CURRENT_USER = &H80000001
strComputer = "."
strKeyPath = "Control Panel\Desktop\WindowMetrics"
strEntryName ="AppliedDPI"
Set objReg=GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & _
    strComputer & "\root\default:StdRegProv")
objReg.GetDwordValue HKEY_CURRENT_USER, strKeyPath, strEntryName, strValue
Wscript.Echo strValue, "DPI"

The following solution can be integrated a bit easier into a Sikuli script, because you do not need an extra .vbs script file.

It uses the reg command.

import os
regKey = r"HKCU\Control Panel\Desktop\WindowMetrics"
regField = "AppliedDPI"
cmd = 'reg QUERY "%s" /v %s'%(regKey, regField)
result= os.popen(cmd).readlines()
print eval(result[-2].strip().split()[-1]), "DPI"

The last statement builds on the knowledge, how the output of the reg command looks like, and prints the DPI as decimal value.