The present invention discloses an inside-container liquid volume measuring method and device based on acoustic detection. The method comprises the steps of forming a cavity inside a container, the cavity meeting the configuration that acoustic waves inside the cavity only can be transmitted inside the cavity; transmitting acoustic waves into the cavity; receiving the acoustic waves reflected by a inner wall of the cavity and a liquid level; and acquiring a volume of a liquid inside the container based on an attenuation coefficient of the reflected acoustic waves. With adoption of the method and the device, the volume of the space can be directly measured, no restrictions are set to the shape of the container, the method and the device are applicable to containers with irregular cavities, requirements for smoothness of the liquid level and placing postures of the container are low, the application range is wide, the structure is simple, the size is small, container sealing and liquid amount measuring are combined together, and the usage is very convenient.