The invention provides a soft nonmetal material deformation measuring device and method. When in use, the soft nonmetal material deformation measuring device connects a deformation visualizing devicewith a soft nonmetal material, when stamping is conducted at a low speed in a high-pressure closed container, the soft nonmetal material deforms, a connection part drags a sliding block in the deformation visualizing device, and through a deformation depicting device, a deformation record of the soft nonmetal material is recorded on a deformation recording device. After stamping is finished, the deformation visualizing device is taken out, displacement is measured after visualization, and the measured displacement is the deformation quantity of the soft nonmetal material. The soft nonmetal material deformation measuring device is simple in structure, easy to operate and wide in application range and can meet the requirements of measuring the deformation quantity of the soft nonmetal material in a high-pressure closed environment or in the environment which is not suitable for traditional strain sensor installation.