High power LED is a kind of ideal green lighting source, which owns longer life, higher efficiency and lower electricity power consumption than incandescent lamps and fluorescent bulbs. Constant current driver is the most key factor for high power LED’s premium properties. Based on the specific chip LM3478, a novel Boost DC/DC converting circuit to drive LED was proposed. The whole circuit structure was simple, and owned high reliability with over current protection. The circuit operates continuous current mode (CCM), with normal supply voltage 12V. The constant output current is 700mA, which can drive two-row LED series, 5 LEDs at least each series. The test results show that the electricity efficiency is up to 93.20% and that the output current deviation is 7.71%. The operating temperature range is -40~+125°C.