In a flash memory device and a bit line voltage control method thereof a circuit capable of reducing the change in a voltage of a bit line during programming. The flash memory device includes: a flash memory cell, a source of which is connected to a source line, a drain of which is connected to a bit line and a gate of which is connected to a word line; a word line voltage generation circuit connected to the word line, for generating and providing a word line voltage to the word line; a program current generation circuit connected to the bit line, for generating and providing a program current to the bit line; and a bit line voltage clamp circuit connected to the bit line and the word line, for sensing a voltage of the bit line and controlling a bias current of the word line voltage generation circuit to thereby control a voltage of the bit line, during a programming operation of the flash memory device. Therefore, it is possible to enhance program efficiency and reduce program disturbance by constantly maintaining the voltage of the bit line to a desired voltage using a bit line voltage clamp circuit during programming.