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