To probe the electron density distribution of the plasma,double-frequency grating shearing interferometry based on the soft X-ray laser technology is developed.The 13.9 nm Ni-like Ag soft X-ray laser is used as a probe to make attempt on the diagnosis of laser produced plasma from a planar gold wafer target.Clear interference fringes image is achieved,which fully demonstrates the practicability of this technology.However,there are some problems such as the unclear target surface in the image.Analysis indicates the main reasons of these problems and a reasonable solution is proposed to improve this technology.