In recent years, the electrical characteristics of WSe2 field-effect transistors (FETs) have been widely investigated with various dielectrics. Among them, being able to perfectly tune the polarity of WSe2 is meaningful and promising work. In this work, we systematically study the electrical properties of bilayer WSe2 FETs modulated by ferroelectric polymer poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)). Compared to traditional gate dielectric SiO2, the P(VDF-TrFE) can not only tune both electron and hole concentrations to the same high level, but also improve the hole mobility of bilayer WSe2 to 265.96 cm2 V-1 s-1 under SiO2 gating. Its drain current on/off ratio is also improved to 2 × 105 for p-type and 4 × 105 for n-type driven by P(VDF-TrFE). More importantly, the ambipolar behaviors of bilayer WSe2 are effectively achieved and maintained because of the remnant polarization field of P(VDF-TrFE). This work indicates that WSe2 FETs with P(VDF-TrFE) gating have huge potential for complementary logic transistor applications, and paves an effective way to achieve in-plane p-n junctions.