Abstract: Traditional adaptive weighting factor can improve the resolution and contrast of ultrasound images,but speckle pattern of background image is broken.Therefore,Subarray Difference Factor(SDF) was proposed to improve the image quality.The factor is used for conventional line-scan ultrasound imaging.It applies the subarray smoothing on the echo signals received by the transducer array to obtain mean values which can represent the intensity of high coherence components.Then,the difference is used to get the differences of the echo signals received by adjacent elements.Finally,SDF is used to weight the Delay And Sum(DAS) output.Simulation and phantom experimental results indicate that SDF(L=8) can improve resolution and yield improvements of 62.9% and 74.7% in contrast ratio,respectively,compared with the DAS beamformer.In comparison with Coherence Factor(CF),Generalized Coherence Factor(GCF),and signal mean-to-standard-deviation factor(SMSF),SDF generates a better background speckle quality with Speckle Signal-to-Noise Ratio(SSNR) improvements of 36.8%,5.7%,26.2% in simulation,and 48.6%,17.0%,20.9% in phantom experiment,respectively.This indicates the effectiveness of the SDF to improve ultrasound image quality.