Abstract: The distributed aperture coherent radar system consist of multiple spatial division radar and can realize signal level detection of target under unified control. It can be used in many area, such as air defense and anti-missile, early-warning detection, precision tracking and space surveillance. This paper carried out a technical research of distributed aperture radar coherent detection in early-warning area. First, the principle of early-warning detection based on Multiple input Single Output system and Multiple input Multiple Output system were given. Then this passage analyzed the detection performance from two aspects including detection power and detection probability. Results showed that detection power and detection probability were obvious improved by using coherent synthesis processing. On this basis, we built a low frequency Two Input Single Output early warning coherent synthesis test system and through coherent synthesis test of aircraft target we validated the performance advantage of distributed aperture radar coherent detection in early-warning area .