Atunable plasmon-assisted electrochemiluminescence (ECL) strategy is reportedusing concave Au nanocubes (Au CBs) for rapidly accelerated fibrosarcoma B-type (BRAF) detection. Concave Au CBs exhibit a strong surface plasmon coupling (SPC) effect between its sharp apexes and edges. The high spectral overlap with graphite phase carbon nitride quantum dots (g-C3N4 QDs) is achieved by tuning surface plasmon absorption peak of the concave Au CBs. It maximizes the SPC effect and enhances the ECL signal of g-C3N4 QDs 3-fold. The SPC effect of Au CBs is twice as high as with Au NPs. We also employed a toehold-mediated strand displacement (TMSD) strategy for sensitive target recycling amplification. Under optimal conditions, this sensor can determine BRAF gene from 1pM to 1nM with a detection limit of 3.06 × 10-5nM (S/N = 3) and RSD 3.67%. With the aid of the TMSD strategy and tunable plasmon-assisted ECL sensing mode, this sensor also exhibits goodanalytical performance in human serum with satisfactory recovery of 90.2~109%. The proposed strategyprovides a promising method to effectively enhance spectral overlap and detect BRAF gene.