Abstract: This paper describes several fundamental problems of the development of LPI radar. The LPI performances related to the characteriztics of target, radar and Elint receiver are analyzed. Then the interception range of radar radiation by Elint receiver for several representative radars is calculated. The LPI measures and its gain are commented. The concept of "LPI Effect Threshold" is proposed. The gain of spread spectrum technique is analyzed. In the end, It is pointed out that LPI Radar is an important radar structural reform and the strategy of two development steps is suggested.