Abstract: The back-streaming white neutrons (Back-n) at Chinese Spallation Neutron Source (CSNS) are of great significance in many fields, such as neutron nuclear data measurement and nuclear technology application. A beam monitor composed of a boron-plated micro mesh gaseous structure (Micromegas) detector was carried out to monitor neutron profile, intensity and energy of the white neutron beam. The neutron time-of-flight (TOF) was measured to obtain energy information. A waveform sampling electronics system based on application-specific integrated circuit (ASIC) chips with switched capacitor arrays (SCAs) was applied to achieve the low-noise amplification, filtering and waveform digitization of 128-channel Micromegas detector anode strip signals. And the readout system also achieved real-time measurement of waveform-over-threshold moment in the field programmable gate array (FPGA) chip. The neutron TOF range is from 650 ns to 10 ms, and the time resolution of the electronics is better than 10 ns. Based on the experiments on CSNS Back-n neutron beam, the neutron beam profile and 10.65 μs 10 ms TOF spectrum were successfully reconstructed, and the corresponding neutron energy range is about 0.16 eV-0.14 MeV. The resonance absorption spectra of ⁵⁹Co and ¹⁸¹Ta absorbers were also measured. These testing results verify the function of the readout electronics system and the accuracy of the TOF measurement.