The accident, which resulted in a five-vehicle pile-up, occurred at around 1am on a bypass road in Tambon Na Katam, Tha Sae district.
Police said the Bangkok-bound trailer truck, which was carrying plywood, was speeding when it crashed into the buses.
The truck driver, Prasit Pakdee, 34, was pronounced dead at Chumphonkhetudom-sakdi Hospital.
The 14 injured were bus passengers.
A Toyota Vios sedan and a Toyota pickup were also caught up in the accident, which affected traffic flow for hours . It was reported that the traffic congestion was 10-kilometre-long.