Structure properties of cell, especially at nanoscale, have shown great potential in early cancer diagnosis and screening. The research has shown that spatial-domain low-coherence quantitative phase microscopy (SL-QPM) can obtain the optical markers which related to the subtle change of nanoscale structure. There is a complex nonlinear relationship between the optical markers and the nanoscale structure parameters. In this paper, a theoretical model of backscattering spectrum of SL-QPM is built with one dimensional Gaussian random field model with one dimensional multilayer dielectric slab model. The result shows that the simulation spectrum matches well with the experimental result. Then the numerical analysis is presented on a series model of histology slides with various known structure properties. We validated that the optical makers of SL-SQM (the average phase, the standard deviation of phase, the average amplitude, the standard deviation of amplitude, the fluctuation ratio) can detect the subtle change of the cell structure( the average refractive index, the variation of refractive index, the spatial correlation length). It provide theoretical basis for the early cancer detection based on SL-QPM.