Abstract: In order to investigate the difference of formaldehyde residue in different parts of dried Lentinus edodes,acetylacetone spectrophotometric method was optimized in this study. The effects of different factors on the determination of formaldehyde residue of dried Lentinus edodes by acetyl acetone spectrophotometric method were studied by single factor experiment with the factors of particle size,soaking temperature,soaking time and phosphoric acid usage,and orthogonal test was also employed to optimize the detection method. Single factor experiment showed that the residue of formaldehyde increased first and then decreased with the increase of particle size,soaking temperature,soaking time and phosphoric acid usage. The orthogonal experiment indicated that the soaking temperature had the most significant effect on formaldehyde residue,the best extraction condition was A₂B₂C₃D₁,that was the particle size 0.710 mm,soaking time 4 h,soak temperature 40℃,phosphoric acid usage amount 5 mL,and under this condition,formaldehyde residue could reach 1.507 mg/g. The results of the experiment showed that the formaldehyde residue in pileus was higher than that in stipe.