In this paper, the combined effects of cycling endurance and radiation on floating gate memory cell are investigated in detail, the results indicate that: 1.The programmed flash cells with a prior appropriate number of program and erase cycling stress exhibit much smaller threshold voltage shift than their counterpart in response to radiation, which is mainly ascribed to the recombination of trapped electrons (introduced by cycling stress) and trapped holes (introduced by irradiation) in the oxide surrounding the floating gate; 2.The radiation induced transconductance degradation in prior cycled flash cell is more severe than those without cycling stress in both of the programmed state and erased state; 3. Radiation is more likely to induce interface generation in programmed state than in erased state. This paper will be useful in understanding the issues involved in cycling endurance and radiation effects as well as in designing radiation hardened floating gate memory cells.