Abstract: This paper introduce the primary factor effect on the energy efficiency of linear transformer driver (LTD). Through the PSpice simulation, resistor representing the core losses and magnetizing inductance affected on the pulse which output by forming network after LTD was discussed. A test stand was developed to measure the energy efficiency of LTD. Based on the test stand, a series of experiment was carried out by changing mean length magnetic path and effective core area. The experimental results indicate that the energy efficiency of LTD would increase 6% when the ratio of mean length magnetic path to effective core was double based on the pulse forming network with an impedance 5Ω, pulse width 300ns. According to the experimental results, decrease the mean length magnetic path will increase the energy efficiency of LTD when the effective core area was fixed on.