Abstract: A small size fiber-optic electric field sensor for measurement of electromagnetic pulse(EMP)in small volume is developed.The influence of the sensor structure on the tested field and the equivalent antenna capacitance are analyzed by CST2011 softuare.The relationship of the bandwidth and the sensitivity with antenna structure and load impedance are discussed.Design parameters are defined based on the analysis results.A conformal sensor structure is utilized to act both as the dipole antenna and the shielding enclosure.It can be used for measurement of both nuclear and lightning EMP.The balanced structure of the sensor makes it suitable for free-field measurement in EMP test and calibration.