Just found one example of Xorg.conf for dual monitor using on laptop. Post it here and check it in future.
For dual-monitor, we need two device, monitor and screen section. And there are two ways to set up dual monitor. "Clone or merging"
Section "Device"
Identifier "intel"
Driver "i810"
Screen 0
BusID "PCI:0:2:0"
Option "VBERestore" "true"
VideoRam 131072
Option "BackingStore" "true"
Option "BusType" "PCIE"
Option "NoAccel" "false"
Option "DRI" "true"
Option "MonitorLayout" "CRT,LFP"
EndSection
Section "Device"
Identifier "Device1"
Driver "i810"
Screen 1
BusID "PCI:0:2:0"
# Option "VBERestore" "true"
VideoRam 131072
Option "BackingStore" "true"
Option "BusType" "PCIE"
Option "NoAccel" "false"
Option "DRI" "true"
Option "MonitorLayout" "CRT,LFP"
EndSection
Section "Monitor"
Identifier "Generic Monitor"
Option "DPMS"
HorizSync 28-64
VertRefresh 43-60
EndSection
Section "Monitor"
Identifier "AL1914"
Option "DPMS"
HorizSync 31-81
VertRefresh 56-75
EndSection
Section "Screen"
Identifier "Default Screen"
Device "intel"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 16
Modes "1280x768"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1280x768"
EndSubSection
EndSection
Section "Screen"
Identifier "Secondary Screen"
Device "Device1"
Monitor "AL1914"
DefaultDepth 24
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
SubSection "Display"
Depth 24
Modes "1024x768"
EndSubSection
EndSection
Section "ServerLayout"
Identifier "Dual-monitor Layout"
Screen 0 "Default Screen"
Screen 1 "Secondary Screen" RightOf "Default Screen"
# Option "Xinerama" "on"
Option "Clone" "On"
InputDevice "Generic Keyboard"
InputDevice "Configured Mouse"
EndSection
Section "DRI"
Mode 0666
EndSection