Abstract: Optical fiber electric field sensors have many advantages such as immune to electromagnetic interference and fast response dynamics, thus this type of devices has great potentials in the field of condition monitoring and insulation status diagnosis of power equipment. The existing sensors are generally composed of many discrete components, which results in low coupling efficient, high loss, and low sensitivity. Moreover, temperature cross-sensitivity is a big issue when comes to practical applications. To counterbalance the above drawbacks, we proposed a new type of optical fiber electric field sensor in which a special functionalized fiber is utilized to replace conventional discrete components. The polarizer as well as waveplate are integrated as fiber-in-line structure, consequently the shortcomings of unstable structure and low performance caused by alignment accuracy and coupling efficient between discrete components can be avoided. Additionally, temperature cross-sensitivity can be suppressed via cascading two crystals orthogonally. The experimental results show that the measurable frequency range covers 50 Hz to 200 MHz and the temperature cross-sensitivity is as low as 0.1%/℃. Thanks to the features of compact size, high stability, and broadband measurement range, the proposed sensor can be used for very fast transient overvoltage (VFTO) measurement of power equipment.