The calculated distance (air line) between Siem Reap and Smach Mean Chey is approximately 137 miles respectively 221 kilometers.
By car or train, the actual journey to Smach Mean Chey is certainly longer, as only the direct route (as the crow flies) between Siem Reap and Smach Mean Chey has been calculated here.
Air line (approximately)
221 kilometers
119 nautical miles