In this study, we examined the microwave power transfer to sensors in car engine compartment. First, we calculated the transmission efficiency in free space. We changed a transmission distance, and confirmed a theoretical limit value of the transmission efficiency in free space. Second, we simulated the transmission efficiency using the cuboid engine compartment model. From simulation results, we confirmed that transmission efficiency was increased by the multiple reflections and that transmission efficiency was decreased by the engine between transmitting (Tx) and receiving (Rx) antennas. Finally, we simulated transmission efficiency using the real engine compartment model. Changing the direction of the antennas, and obtained 2.8% of the highest transmission efficiency in the required antenna position. In addition, changing the position of the Tx antenna, we obtained 7.2% of the highest transmission efficiency.