An adjustable magnetic field generating device comprises an insulating casing, a signal generator, a power amplifier, an adjustable magnetic heat coil, an oscilloscope, a magnetic field measuring instrument, a temperature measuring instrument and a sample cell with a condenser pipe, wherein the signal generator, the power amplifier, the adjustable magnetic heat coil, the oscilloscope, the magnetic field measuring instrument, the temperature measuring instrument and the sample cell are arranged in the insulating casing; the adjustable magnetic heat coil comprises two mutually independent coils and an adjustable-distance frame; a fixed groove is fixed in a fixed base; coil distance adjusting rods are arranged at two ends of the fixed groove; the coils are connected with the coil distance adjusting rods through retaining clips; the sample cell is arranged between the two coils; the signal generator is used for generating signals with different waveforms, and the signals are amplified and adjusted by the power amplifier and then are transmitted to the coils; the magnetic field measuring instrument is used for measuring the magnetic field intensity generated by the coils; the oscilloscope is used for measuring signals exerted on the coils; and the temperature measuring instrument is used for measuring magnetic heat generated by samples in the sample cell in real time. The adjustable magnetic field generating device has the characteristics of simple components, high accuracy, high magnetic field intensity, good adjustability and controllability, high applicability and the like.