Memristor crossbar array is promising for realizing artificial neural networks. Wire resistance in crossbar array is one of the factors that degrade the performance of memristor crossbar circuit. In this article, we analyze the effect of wire resistance on the output voltage of crossbar array and add the differential amplifier circuits to the crossbar array to mitigate the voltage variation caused by wire resistance. In memristor crossbar array, the voltage variation caused by wire resistance is proportional to the length of metal line. In addition, two adjacent columns have the same voltage variation. Under these observations, a differential amplifier circuit is used to compensate the voltage variation of two adjacent columns. When wire resistance is 2.5Ω, the recognition rate is as low as 76%. However, if the differential amplifier circuits are added to the crossbar circuits, the recognition of the crossbar circuit is as high as 97%. Adding the differential amplifier circuit to memristor crossbar circuit can mitigate the impact of wire resistance in memristor crossbar circuit significantly