In　order　to　study　the　influence　of　the　quality　and　content　of　fly　ash　on　the　cracking　behaviors　of　concrete,　the　modified　flat　type　specimen　was　used.　The　effects　of　particle　size　distribution　and　oxide　component　of　fly　ash　on　the　optimal　content　for　the　cracking　behavior　of　high-flowing　concrete　were　studied　by　grey　connection　analysis.　The　results　indicate　that　when　the　particles　size　are　smaller　than　20.4m,　there　are　positive　effect　on　the　optimal　content　of　fly　ash　on　the　cracking　behavior　of　high　flowing　concrete.　Properly　increasing　the　content　of　MgO,　K2O,　CaO　and　SO3　and　decreasing　the　loss　on　ignition　may　raise　the　optimal　content　of　fly　ash　on　the　cracking　behavior　of　high-flowing　concrete.