Purpose: A kind of sine wave magnetic field generator with the extremely low frequency (ELF) is developed, the frequency and intensity of the magnetic field can be adjusted, and has been easily used in Bio-experimental study. Methods: At first ,we design a DC power supply which provide DC voltage to other chips,then the signal generated by single chip ma-chine system and the power amplifier combined by discrete components, it provides current 0 mA～136 mA.The current coil is designed by experiment's required,the size or turns is changed, the magnetic field intensity is changed too. Results: The fre-quency of the device output is 0 kHz-25 kHz with the intensity in the range of 0 mT～10 mT within which the continuous lin-earity is adjustable. Power sources are less than 30 W ,which can work for long.This device performs reliably and the measured values in accord with the theoretical values and has been used in the experiment of magnetic biological effect. Conclusions: The experiment results indicate that there exist the effects of ELF sine wave magnetic field upon potassium current of neurons, and that such bioeffects vary with the intensity and frequency of the field.Also,there may exist window effect areas.