[Objective] To explore the tolerance characteristic of selenium of Hypsizygus marmoreus mycelium strains. [Methods] To determine the average growth rate of mycelium at different concentrations of selenium by using the plate culture method and fitting the relationship between selenium and mycelial growth rate. Record the mycelium germination, the morphological characteristics of colony and do the restoring culture to verify. Using microscopic to observe the effect of selenium on the hyphae branch, size, lock-like joint morphology and surface structure. [Results] The results of experiment showed that when exogenous selenium concentration ≤50 mg/L, it promoted the growth of mycelium. The promoting effect vary in different strains, but compared to Control Check (CK), there is no significant difference (P>0.05). When exogenous selenium concentration ≥75 mg/L, the growth of H. marmoreus was inhibited. The maximum tolerance concentration of selenium is 150–200 mg/L. Restoring culture showed that this kind of inhibition could be restored; selenium concentration and the average growth rate accords with mycelium Cubic regression curve and the coefficient of determination (degree of fitting) is large. The results of microscopy observation indicated that when the concentration of exogenous selenium is low, the mycelia showed the following characteristic: even thickness, robust and full, more branches, smooth surface and distinct lock-like joint clear structure. At higher concentrations of exogenous selenium, thickness of the mycelium is irregular and it shrinked to long flat strip. The lock-like joint structure collapsed and wizened, the surface is uneven and became bamboo-like structure. The tip part of hyphae was gradually substituted by spherical conidia and some branches even were completely alienated into conidia or chlamydospores. [Conclusion] when the selenium concentration ≤50 mg/L, it has a promoting effect on the growth of mycelium; when selenium concentration ≥75 mg/L, it inhibited the growth. High concentration of selenium has toxic effects on the mycelia, but the toxic effects are reversible.