We construct the CR invariant canonical contact form can(J) on scalar positive spherical CR manifold (M,J), which is the CR analogue of canonical metric on locally conformally flat manifold constructed by Habermann and Jost. We also construct another canonical contact form on the Kleinian manifold Ω(Γ)/Γ, where Γ is a convex cocompact subgroup of AutCRS2n+1=PU(n+1,1) and Ω(Γ) is the discontinuity domain of Γ. This contact form can be used to prove that Ω(Γ)/Γ is scalar positive (respectively, scalar negative, or scalar vanishing) if and only if the critical exponent δ(Γ)<n (respectively, δ(Γ)>n, or δ(Γ)=n). This generalizes Nayatani’s result for convex cocompact subgroups of SO(n+1,1). We also discuss the connected sum of spherical CR manifolds.