Conventional Brillouin optical time-domain reflectometer (BOTDR) system faces challenges in accurately measuring temperature or strain variations in sub-pulse event zones. To address this technical challenge, a joint demodulation scheme based on Brillouin frequency shift (BFS) and power is proposed to achieve length, temperature, and strain measurements in sub-pulse event zone. By utilizing the principle of pulse superposition, a linear relationship has been established between BFS, scattered light power, event zone length, and temperature. Both numerical simulation and experimental validation have confirmed the validity of this linear relationship. Ultimately, with a pulse width of 100 ns, in the measurement experiment where the actual length of the event zone is 3 m and the temperature is 52 ℃, measurements of 2.91 m for length and 51.68 ℃ for temperature of event zone are achieved at the end of a 10 km fiber, resulting in a significant improvement in measurement accuracy compared to the 32.63 ℃ measured using traditional BOTDR demodulation scheme. The proposed scheme overcomes the limitations of pulse width, enabling the measurement of sub-pulse length event zones and providing a novel approach for enhancing the spatial resolution of BOTDR systems.