The ASTM D3404-15 standard guide provides a standardized method for the measurement of matrix potential in the encapsulated area using a tensiometer. The matrix potential in the encapsulated area is an important indicator of soil water status and is essential for soil water management, irrigation control, and environmental scientific research. The standard describes in detail the correct installation, operation steps, and data interpretation methods of the tensiometer to ensure the accuracy and conformity of the measurement. By following this standard, users can obtain reliable matrix potential data in the encapsulated area, so as to better understand the soil water dynamics and related ecological processes. This guide is suitable for agriculture, environment monitoring, and water resources management. It provides scientific basis and technical support for related research and practice.