Achieving high heat-resisting room temperature phosphorescence (RTP) performance and robust white emission from pure small molecules is a meaningful but challenging work. Herein, a simple donor-acceptor (D-A) molecule, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole (CzBtrz), was investigated. This simple molecule not only exhibits multiple emissions including white light, thermally activated delayed fluorescence (TADF) and ultralong RTP with a lifetime of 988.54 ms at 545 nm, but also shows superhigh heat-resisting phosphorescence property which can maintain stability in a large temperature region from 77 to 350 K (ΔT = 273 K), exceeding those of other RTP systems. Meanwhile, this molecule shows the time-evolved dynamic RTP. The experimental and theoretical analyses from CzBtrz crystal demonstrate that the intramolecular charge transfer (ICT) interaction and molecular stacking play an important role in the generation of RTP. Therefore, this work provides an efficient strategy to design ultrahigh heat-resistant RTP, ultralong RTP and single-phased white-light emitting materials.