Abstract: In order to improve the utilization efficiency of classified tailings and realized the effective application of cemented paste backfill in mine， the strength test of different cement-tailing ratio （1∶6， 1∶12， 1∶20） and different mass concentration （65%，70%，75%） was designed based on the analysis of physicochemical properties for the unclassified tailings in Jidong area， in combination with X-ray Diffraction （XRD） analysis and scanning electron microscope （SEM） analysis， to study the effect of tailings grain on early strength of cemented paste backfill （CPB） ， hydration products and pore structure. The research shows that the tailings particle size has a significant influence on early strength of CPB， that the fit to the cement hydration can be effectively improved when the tailings particles a certain fineness， as the particle size decreases， the early strength of the CPB is greater， and it is more sensitive to changes in the cement-tailing ratio and mass concentration. Based on the characteristic indexes of tailing， an early strength prediction model about tailing particle size， cement-tailing ratio and mass concentration was established， the correlation coefficient R>0.95， the error rate <2%， so the correlation is good， and the prediction result is reliable. It is suggested the cement-tailing ratio of cemented unclassified tailing backfill （CUTB） in Jidong area in the range of 1∶6~1∶8， and the mass concentration is higher according to the working conditions of the filling system. Under the same conditions of the mix proportion scheme， as the particle size of the tailings decreases， the C—S—H gel generated during the early hydration of the CPB， and the pore size and number also decrease， the macro behavior is the increase in strength. Finally，the test was designed in an iron mine in Jidong area，so as to further verify the reliability of the strength prediction model， the average error of the results was 3.49%， indicating that the model can accurately predict the early strength of CPB AND provide a basis for iron mine backfill design.

Key words: filling mining, tailings particles size, strength, prediction model, hydration products, pore structure