The calculated distance (air line) between Dien Bien Phu and Luang Namtha is approximately 109 miles respectively 175 kilometers.
By car or train, the actual journey to Luang Namtha is certainly longer, as only the direct route (as the crow flies) between Dien Bien Phu and Luang Namtha has been calculated here.
Air line (approximately)
175 kilometers
94 nautical miles