This　article　studies　the　Dirichlet　eigenvalue　problem　for　the　Laplacian　equations　Δu　=-λ　u,　χ∈　Ω,　u=0,　δ∈Ω,　where　Ω　⊂　Rn　is　a　smooth　bounded　convex　domain.　By　using　the　method　of　appropriate　barrier　function　combined　with　the　maximum　principle,　authors　obtain　a　sharp　lower　bound　of　the　difference　of　the　first　two　eigenvalues　for　the　Dirichlet　eigenvalue　problem.　This　study　improves　the　result　of　S.T.　Yau　et　al.　©　2007　Wuhan　Institute　of　Physics　and　Mathematics.