A low-power 433MHz transmitter is designed using 0.18um CMOS process for battery-less TPMS. It is mainly composed of a PLL frequency synthesizer and a PA, and the transmitter is achieved in a fully integrated chip except for choke and output match inductor of PA. Based on post-simulation, locked time and phase noise of the PLL are respectively about 60us and -105dBc/Hz@300kHz, the power consumption of transmitter is 25mW when output power of PA is 7dBm. The area of the whole transmitter is 1mm x 1mm, including ESD pads. The sample chip is under fabrication.