The propagation of intense femtosecond laser pulses(50 fs,10 16 w/cm2) in Ar gas and middle-size Ar clusters is modelled by solving 3D propagation equation numerically.The results show that the intense femtosecond laser pulses propagating in Ar gas will experience ionization-induced modulations, including spectral blueshifting and beam refraction,while self-focusing may occur for the intense femtosecond laser pulses propagating in Ar clusters.