The samples of the China Spallation Neutron Source (CSNS) Engineering Material Diffraction Spectrometer (EMD) are very large and have different shapes. The neutron collimation aperture needs to be designed as a pointed-mouth slit to be close to these abnormal components. The main function of the pointed-mouth slit is to provide the beam size is needed by the sample experiment, and ensure that the beam size has high accuracy. The pointed-mouth slit is continuous, and it can be changed according to the experimental requirements. The blade uses enriched boron carbide, which can reduce the deformation of the slit cantilever structure. The slit has a very long mouth, which can approach the special-shaped components and enter into the long tubes. The deformation problem of the cantilever was simulated and analyzed using finite element software. The slit adopts a dual safety design, which can effectively prevent from being damaged by large samples. This slit has been applied to the CSNS engineering material spectrometer. It has made remarkable contributions to residual stress measurement. The application of this slit provides a very important reference for the design of the pointed-mouth slits.