It happened in the 16400 Block of Wood Drive on Monday evening.
Firefighters were called to the area just before 6:30 p.m. when the fire erupted in the trailer, said the Channelview Fire Department.
CPR was administered to a man and a woman inside the trailer, and they were both taken to a nearby hospital, according to the Harris County Fire Marshal's Office.
The man died shortly after in the hospital, and the woman remains in serious condition, according to authorities.
Authorities confirmed Tuesday afternoon that the fire was caused by a water heater.