The absence of any confirmative signals from extensive DM searching motivates us to go beyond the conventional WIMPs scenario .
The feebly interacting massive particles ( FIMPs ) paradigm provides a good alternative which , despite of its feebly interaction with the thermal particles , still could correctly produce relic abundance without conventional DM signals .
The Infrared-FIMP based on the renormalizable operators is usually suffering the very tiny coupling drawback , which can be overcome in the UltraViolet-FIMP scenario based on high dimensional effective operators .
However , it is sensitive to the history of the very early Universe .
The previous works terminates this sensitivity at the reheating temperature T _ { RH } .
We , motivated by its UV-sensitivity , investigate the effects from the even earlier Universe , reheating era .
We find that in the usual case with T _ { RH } \gg m _ { DM } , the production rate during reheating is very small as long as the effective operators dimension d \leq 8 .
Besides , we consider the contribution from the mediator , which may be produced during reheating .
Moreover , we study the situation when T _ { RH } is even lower than m _ { DM } and DM can be directly produced during reheating if its mass does not exceed T _ { MAX } .