In this paper, a novel high-sensitivity broadband rectifier is proposed aiming at ambient radio frequency (RF) energy harvesting. Traditionally, voltage doubling rectifying circuit is used to design high-sensitivity rectifier. But when the input power is lower, the rectifying efficiency is significantly reduced. Therefore, an improved parallel half-wave rectifying circuit is proposed in this article which can convert RF energy in the whole period. And the proposed rectifying circuit can work better in lower power environment and has a higher efficiency level. Besides, the impedance match is also important component of rectifier. Due to the nonlinearity and complexity of rectifying circuit, achieving wideband matching network is a challenge. Thus, a design approach of broadband impedance circuit is given in this study. Combining with the proposed highsensitivity rectifying circuit, a high-sensitivity wideband rectifier can be generated, when the input power is -15 dBm, -20 dBm, -25 dBm, the efficiency is 43%, 32%, 20%, respectively. Finally, a second-order wideband rectifier with high sensitivity is realized, and the range of bandwidth can cover four main frequency bands of GSM 900 MHz, GSM 1800 MHz, UMTS 2100 MHz, WLAN 2400 MHz. To verify the validity, the rectifier is fabricated and measured, and the measurement has a good agreement with simulation results.