Due　to　a　large　number　of　studies　on　cross-evaluation　strategies,　the　theoretical　problem　of　DEA　cross-efficiency　approach　has　been　transformed　from　the　non-uniqueness　of　the　optimal　solution　to　the　relative　uniqueness,　because　the　existing　cross-evaluation　strategies　can　only　reduce　the　possibility　of　non-unique　solutions,　but　cannot　prove　the　existence　of　a　unique　optimal　solution.　This　paper　illustrates　the　relative　uniqueness　of　optimal　solution　of　the　cross-efficiency　approach　with　traditional　cross-evaluation　strategies,　and　the　graphic　method　and　theoretical　analysis　are　used　to　explain　the　reasons　of　relative　uniqueness.　Based　on　the　data　characteristic　of　inputs　and　outputs,　the　weight　priority　rule　is　made　for　constructing　the　new　cross-evaluation　strategy,　and　its　optimal　solution　is　proved　to　be　unique.　In　addition,　the　weight　priority　strategy　can　also　be　introduced　into　traditional　strategies　as　a　supplementary　strategy,　and　then　the　unique　optimal　solution　can　be　obtained　on　the　premise　of　preserving　the　characteristics　of　traditional　strategies.　In　general,　this　paper　solves　the　non-uniqueness　and　relative　uniqueness　problem　of　optimal　solution　in　the　DEA　cross-efficiency　approach,　and　then　the　reliability　and　robustness　of　the　approach　are　thus　improved.