Abstract: In the urban road environment， the signal-to-noise ratio of the target echoes such as pedestrians and roadblocks are low， which leads to low detection performance for conventional automotive radar. In this paper， the distributed coherent array is applied to the automotive radar， and the target signal-to-noise ratio is improved through the coherent accumulation of multiple radar echoes， thereby enhancing the detection performance of automotive radar. Coherent parameter estimation is the key to realize coherent accumulation of distributed automotive radar. However， non-ideal orthogonal of inter-pulse phase encoding waveform will lead to the low accuracy of traditional coherent parameter estimation methods. To solve above problem， a coherent parameter estimation method is proposed for the stepwise estimation of delay parameters and phase parameters. First， the echoes of each channel are separated according to their orthogonality. Then， the delay parameters between channels are estimated based on the position of the target. Afterwards， the delay parameter compensation is used. Finally， after the target position of each channel is aligned， the phase parameters of each channel are estimated. Simulation and experiment show that compared with traditional coherent parameter estimation methods， the phase parameter estimation accuracy of the proposed method is higher.