The process of galaxy formation alters the phase-space distribution of the dark matter and stellar components of the Milky Way halo. Debris from accretion is apparent as spatial overdensity at the beginning. After several billion years, those pieces of debris are spread over several tens of kpc. Thus, one cannot expect to find many of the halo streams predicted as spatially coherent structures in the solar neighborhood. However, the phase-space structures of those streams provide hints about their common origin. The origins of these halo streams play an important role in understanding the formation of our Milky Way. In this talk, I will present our detections of new evidence for a merging history of our Milky Way. Simulations predict one dwarf galaxy might correspond to multiple streams detected in phase space and there should be hundreds of streams in the Galactic halo. LAMOST survey provides an unprecedentedly large sample and will contribute to more and more detections of halo streams.