A number estimation technique is proposed to solve and decide the appropriate number of the independent components of Independent Component Analysis (ICA) in eddy current pulsed thermography (ECPT). Based on the physical meaning of the independent components in ECPT, the number estimation of the independent components can be converted into the cluster number estimation of the transient thermal responses. In this paper, the relationship of the number of the independent components and the cluster number of the transient thermal responses will be discussed. The specific clustering process and the cluster number estimation criterion will be introduced. The experimental results are used to verify the validity of the proposed number estimation method.