Structural, transport, and magnetoelectric (ME) properties of delafossite oxides CuCr1-xO2 with 0 <= x <= 0.10 were extensively investigated. The Rietveld refinement shows that the Cu-O bond length decreases with increasing Cr deficiency, indicative of the presence of a mixed valence state of Cu+/Cu2+ and an enhancement of the hybridization between Cu 3d and O 2p orbitals. As a result, it leads to a decrease of room-temperature resistivity by two orders of magnitude. The deduced effective moment for the Cr-deficient samples is larger than the one only taking into account the contribution from Cr3+ with S = 3/2. This demonstrates that Cu2+ is present in the Cr-deficient samples, giving rise to excess holes at the Cu site. Below TN(Cr) ∼ 24 K, the magnetocapacitance [[variant_greek_epsilon](H)-[variant_greek_epsilon](0)]/[variant_greek_epsilon](0) exhibits a distinct field dependence and deviates from the square of magnetization M2. These findings suggest that the ME coupling in CuCr1-xO2 with higher x is modulated by an increase of the spin fluctuations in the CrO2 triangular lattice through the interplay between charge and spin degrees of freedom.