With three kinds of condenser zone plates (CZPs) and pinholes, the linear monochromator transmits soft X-rays of 1.97—5.44nm wavelength range. The soft X-ray diffraction images (i.e. the optical field distribution of the monochromator) were recorded from the combination of CZP32 and a pinhole of 30μm by using positive photoresist under the conditions of an appropriate focusing and a large focusing error. The properties of optical field, such as the radius of Airy pattern and the good spatial coherence region, were also obtained. The experimental results agreed well with the theoretical calculation.