[en] The basic principle and the implement method of bi-directional detector for fuel handling system in 10 MW high temperature gas-cooled reactor were studied. Two inductor coils in parallel connection were used as the sensitive element and two-channel circuit were chosen in the signal sampling circuit, a 89C51 microprocessor was applied as the processing core, the ball-passing signals were acquired on the input port through the mode of circulate scan in the system program and analyzed by the intelligence technology, the function of the bi-directional detection of fuel element was realized