This work uses 2-mode SSHI rectifier to lower the requirement of the input VOC during cold start-up state. A 0.5-V VOC is used as the input, and a 1.27-V VDD is the output voltage. In mode 1, only passive voltage multiplier is working while in mode 2 active SSHI rectifier combined with passive FBR starts to work. The simulated maximum output power of the typical cold start-up circuit FBR is 0.1 μW due to low input VOC and voltage drop of diodes. In our proposed design the output power is 24.5μW with 86.7% flipping efficiency.