The thermal performance of the building envelope significantly affects indoor thermal comfort and operational energy consumption. Biomass envelopes are attracting more attention due to their eco-friendly properties, renewability, and other notable benefits. In this paper, a novel wood fiber-based biomass composite phase change material (PCM) (A-WF/LASA/h-BN) with high thermal storage performance was developed. It encapsulates lauryl alcohol-stearic acid PCM into acetylated wood fibers by vacuum adsorption, with hexagonal boron nitride added to reinforce its thermal conductivity. SEM, DSC, FT-IR, and TG were used to characterize its thermal and chemical properties, and thermal storage experiments were carried out to evaluate its thermoregulation performance. Results show that A-WF/LASA/h-BN is structurally, chemically, and thermally stable as well as having excellent thermoregulation performance. No significant leakage was observed during the experiment. Within the range of 0 to 100°C, the leakage rate was only 1.66%. After 400 thermal cycles, the latent heat of phase change decreased by only 2.63 J·g-1. The appropriate temperature range of the phase change and the high enthalpy of the phase change make it suitable for building envelope applications. Compared with acetylated wood fibers, the peak temperature of A-WF/LASA/h-BN was reduced by 3.09°C, and the peak time was delayed by 7.78 min. Infrared thermal imaging shows the temperature distribution of the A-WF/LASA/h-BN sample is more uniform during the heating up and cooling down process, which indicates a superior ability to suppress temperature fluctuations. The superior composite PCM applied in the envelope can reduce building energy consumption while enhancing indoor thermal comfort.