To reconnoiter targets in a large-scale area independently with onboard reconnaissance equipment was one of the most important applications for UAVs in modern battle field.Focusing on the problem of effectiveness evaluation for UAV when executing reconnaissance tasks,a model was built up for CCD camera,and the advantages and the disadvantages of UAVs in excuting reconnaissance were analyzed.Based on which a model was proposed for evaluating large-range reconnaissance route planning.Then,using this model,the searching pattern of UAV,box-spiral,was improved and the path was analyzed.The improved pattern was verified by a simulation.The effectiveness evaluation model and the improved searching pattern can be taken as a reference for UAVs in taking reconnaissance tasks,which has certain engineering values.