Developing solution-processable deep-blue multiple resonances thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Here, we using a convergent synthesis process successfully developed a series of MR-TADF dendrimers based on C=O/N resonant core (QAO). The alkyl chain alternate-linked functional dendrons not only ensure the narrow-band deep-blue emission but also enable the dendrimers with aggregation-induced emission enhancement (AIEE) properties, which efficiently mitigate the aggregation-induced exciton quenching (ACQ) and obnoxious spectral redshift broadening effect. Notably, the solution-processed deep blue MR-TADF OLEDs achieved a maximum external quantum efficiency (EQE) of 13.5 % and CIE of (0.15, 0.12) with an electroluminescence peak below 450 nm. Further using such dendrimer as a sensitizer for white OLEDs resulted in an optimized high EQE of 18.9 % and a high color-rendering index (CIR) of 81.1 for two and three optical components of white emissions, which are among the highest values of previously reported solution-processed all-fluorescence white OLEDs. This is the first attempt to construct white OLED based on an MR-TADF emitter and the satisfactory results indicate that the flexible dendron engineering strategy can effectively develop high-performance narrow band deep-blue MR-TADF for wide-color gamut display and high CIR white OLEDs.