We download the Large sky Area Multi-Object fiber Spectroscopic Telescope Data Release 8 (LAMOST DR8) low resolution catalog for 6,478,063 AFGK type stars and plot the figures of effective temperature, gravitational acceleration and metal abundance. Some small and medium mass stars are evolved from pre-main sequence or main sequence stage to planetary nebula stage or white dwarf stage by the stellar evolution code MESA. We analyze the observed statistical data and model calculation results, and then obtain some basic conclusions preliminarily. Most red giant and asymptotic giant branch stars with log g less than 0.85 have poor metal abundance. Most hot A type main-sequence stars are metal-rich stars with log g from 3.5 to 4.5. The conclusions are reasonable within a certain error range. The theory of a gap area in the Hertzsprung-Russell diagram for stellar evolutions of medium mass stars is reflected in the statistical plots. The central core hydrogen burning stage and the central core helium burning stage correspond to the peak structures in the statistical plots for gravitational acceleration. The metal abundances among A, F, G and K type stars have a wide distribution. We cannot simply replace the metal abundances of these stars with the metal abundance of the Sun when doing fine research work.