Based on Phyphox App，it uses smart phone to build an experimental device for coupled pendulum．By measuring the change of magnetic induction intensity to indirectly measure the amplitude of the pendulum，the in-phase and anti-phase motion of the coupled pendulum and the coupled strength，the distance between the coupled point and the rotating point are investigated．The beat phenomenon of normal vibration of coupled pendulum is also studied．The results show that in the case of in-phase oscillation，the oscillation period has little relation with the position of the coupled point，while in the case of anti-phase oscillation，the inverse square of the oscillation period has a linear relation with the square of the distance between the coupled point and the inverse square． The transfer of energy between two pendulums can be seen very clearly under the condition of normal vibration． In addition，the relative error between the measured beating period and the theoretical value is 7．9%．