In this paper, we study the spectral efficiency of the uplink multi-user large-scale distributed antenna systems (DAS) with imperfect channel state information. We propose the system model of multi-user DAS and illustrate the necessity of pilot reuse. Then, we derive the sum-rate of the system under pilot contamination. Furthermore, we investigate the asymptotical performance when the number of antennas goes to infinity. To reduce the pilot contamination, we present two novel pilot assignment algorithms to improve the spectral efficiency. Finally, we evaluate our proposed strategies through extensive simulations which show that compared with random pilot reuse, the min-max algorithm shows impressive performance with low complexity.