The k-barrier coverage problem is known as the problem of detecting the intruders by at least k sensors when the intruder moves along the crossing paths from one boundary to another. This paper considers a mobile WSN with demand of k-barrier coverage. To increase the monitoring quality and reduces and balances the energy consumption for each mobile sensor, this paper designs a distributed algorithm aiming at moving fewer mobile sensors with shorter distance for increasing the monitoring quality from (k-1)-barrier coverage to k-barrier coverage. Performance study reveals that the proposed algorithm can efficiently improve the monitoring quality and extend the network lifetime.