Abstract: Objective The heat input Q_UI only briefly describes the source and magnitude of welding energy, without clarifying how the heat absorbed by the weld and base metal is distributed. Methods In this paper, the thermal power P_PR concept based on the amount of filled metal was used to realize prediction of welding heat input distribution and dilution ratio by means of weld size measurement, JmatPro and formula calculation. Results Based on P_PR, the melting base metal area A_mb could be predicted, and its curve change could be divided into three stages, gradual increase zone, rapid increase zone and slow increase zone. Combined with the specific heat capacity of material volume calculated by JmatPro and A_mb prediction formula, the effective welding heat input Q_e under different P_PR could be subdivided. It was found that the heat input of forming weld in the weldable zone only accounted for 31.77% to 34.69%. Conclusion The prediction formula of weld area percentage dilution ratio δ based on P_PR was proposed, and the welding thermal power of weldable zone was 12.69 ~ 47.88 kW/cm², and the dilution ratio was 48.28% ~ 85.03%.