Abstract: TV documentaries with major themes have become an important medium for the public to understand history and culture with their unique perspective and profound social influence. With the progress of communication technology and the improvement of audience's aesthetic demand， the creation of major theme documentaries has gradually changed from simplification to diversification， in which the choice and application of narrative timbre has become an important factor affecting narrative effect. Taking Forging a Lion for Rejuvenation and Steel Backbone as research samples， this study explores the application of diverse interpretation timbre in documentaries with major themes， and reveals the key role of diverse interpretation timbre in enriching emotional expression and enhancing narrative tension. It is found that different timbre types have different functions in narrative structure， and the diversified use of explanatory timbre not only has the value of emotional transmission and atmosphere creation， but also has the value of enhancing narrative tension. This study provides theoretical support for the timbre design of major documentaries， and has practical significance to promote the innovation of documentary creation and improve the communication effect.