In order to prepare ultra-high purity silicon material whose purity is larger than 11N,diameter is larger than 45mm and all performance indices coul d meet the detector level requirements, the Φ(52－65) mm detector level silicon crystal was p repared by vacuum floot zone (FZ) technology. The cause and solution of unstable growth problem,low radial resistiv ity uniformity and swirl defect problems caused by vacuum atmosphere and the inc reasing of crystal diameter are analyzed. The results indicate that Denmark coil with cross slits and steps on its surface is the ideal one for growing Φ>45mm crystals.Increasing the growth and rotation speeds of the mono-crystal is good for decreasing the radial resistivity uniformity,and increasing the rot ation speed is the better option.Increasing the concentricity of thermal field is good for reducin g the swirl defect,its influence on swirl is more remarkable than crystal growth speed,and it is different from Ar atmosphere FZ technology.With the increasing of the refinement times of poly-crystal,the lifetime of mono-crystal will decreas e.The low original concentrations of P,B and metal in poly-crystal are good for enhancing the life time of mono-crystal.To prepare Φ(52－65) mm detector level mono-crystal who se lifetime is longer than 800μs,the poly-crystal silicon lifetime should be longer then 3000μs.