Abstract: The Back-n White Neutron Source is located in China Spallation Neutron Source(CSNS). It aims to measure nuclear data under different neutron energies. The neutron’s energy is obtained by the Time Of Flight(TOF) of neutron. In experiment, the time when proton bunches hit the thick tungsten target is considered as the start point of TOF(T0), and the corresponding electronic signal is used to trigger the whole electronic system. The accuracy fan-out of T0 signal will have a significant influence on the accuracy of the TOF measurement and the synchronization of each channel of electronic system. A two-stage accuracy fan-out method of back-n T0 signal is proposed. The T0 signal from CSNS proton accelerator is fanned out by T0 fan-out module to two underground experiment station through long cable. The fan-out module uses signal pre-emphasis technology to improve the signal transmission quality of T0 signal through more than 100 m long cable and guarantee that the T0 signal has a very fast signal leading edge, so as to ensure the accuracy of time timing. The electronic system takes the advantage of the high-performance backplane resources of the chassis by PXIe, so as to realize the global precision and synchronous fan-out of T0 signal. The experimental results show that the leading edge jitter of the T0 signal distributed by the fan-out module reaches 25 ps, the multi-channel accuracy of the chassis reaches 45 ps, and the measurement accuracy of the TOF can reach 248 ps, which meets the requirements of the measurement accuracy of the neutron time of flight of the white light neutron source.