The development of DC transmission technique is prompting the development of AC/DC hybrid grid. As a new form of the grid, AC/DC hybrid grid faces many challenges one of which is the effect of DC blocking on AC lines. This paper analyses the influence of DC blocking on AC lines. Based on the analysis, a control strategy using wide area information is proposed to avoid the severe overload of AC line after blocking a DC line. The proposed strategy increases the transmission power of normally operating DC line aiming to afford part or all of the transmission task of the blocked DC line. The test result obtained from simulation indicates that the proposed strategy can reduce the overload of AC line after blocking a DC line.