Based on the different failure modes of FRP composites under random vibration fatigue loading, FRP composites are categorized into brittle and ductile types. The study summarizes the damage evolution patterns of these two types of FRP composites under random vibration fatigue loading, with matrix cracking and delamination being the primary damage modes. A new model is proposed to describe the degradation of natural frequency in FRP composites under random vibration fatigue loading, quantitatively accounting for the effects of different damage modes on natural frequency reduction. The applicability of the model is validated using random vibration fatigue test data from two materials of different characteristics: 2D woven ceramic matrix C/SiC composites and 2D woven glass fiber resin-based composites. The results indicate that this model accurately describes the natural frequency degradation behavior of FRP composites under random vibration fatigue loading.