The invention relates to a self-balancing free-piston internal-combustion generator, and belongs to the field of energy source power. The internal-combustion generator comprises free-piston internal-combustion engines, reversing gears and linear generators, wherein every two pistons are fixedly connected by a rack connecting rod to form a piston assembly; generator rotors of the linear generators are perpendicular to the piston assemblies in the free-piston internal-combustion engines; one reversing gear is arranged on one side, far away from motor stator coils, of each rack connecting rod; racks on the rack connecting rods are engaged with the reversing gears; the reversing gears are engaged with racks on the generator rotors; the rack connecting rods are movably connected with the generator rotors by the reversing gears; and the two linear generators and the two free-piston internal-combustion engines are connected by the two reversing gears to form the self-balancing free-piston internal-combustion generator. The internal-combustion generator achieves synchronous motion between the two piston assemblies by the reversing gears; reciprocating inertia forces and moments of the piston assemblies and the generator rotors are balanced; and vibration of a system is eliminated.