In thia paper we described the design and preparation method of Ni-0 multilayer soft X-ray mirrors with emphasis on the thickness monitoring method. The optical coefficients of Ni and C superficial layers at 6328 A are determined by ATR method and so their thicknesses could be monitored by measuring the transmittanoe of the sample at that wavelength during deposition. The depth profile of a sample was analyzed with AES; the diffraction performance at 1.54A and the reflectivities at soft X-ray region of some samples were measured and compared with the theoretical calculations.