Abstract: In order to develop a new type epoxy gel coat to meet the requirements of aeronautical environment, the impact toughness and impact fracture morphologies of epoxy gel coats modified with different molecular weights and different amounts of polyethylene glycol(PEG) at room temperature were investigated. Then, the crack properties of PEG modified epoxy gel coat under thermal shock(-50℃/30 min+90℃/30 min) were mainly investigated by using a simple thermal shock specimen model, and it was verified by analyzing the changing tendencies of thermal expansion and storage modulus etc. The results show that the impact strength of 5wt% PEG-1000 modified epoxy gel coat is enhanced by 31.8% comparing with that of unmodified epoxy gel coat, which reaches the highest value of 4.97 kJ·m^-2. More obvious plastic deformation morphologies appear on the impact fracture surfaces of PEG-1000 and PEG-2000 modified epoxy gel coats, and the impact toughness of gel coats increases. The macroscopic initial crack property of 15wt% PEG-400 modified epoxy gel coat under thermal shock reaches the best, average initial crack needs conducting 10.4 cycles. The properties of crack extension resistance for modified epoxy gel coat are basically improved with the increase of PEG molecular weight and content. However, the crack width will be amplified with the increase of PEG molecular weight.