In this paper, we investigate the dynamics of the following family of rational maps f λ (z) = z 2n − λ 3n+1 z n (z 2n − λ n−1 ) with one parameter λ ∈ C * − {λ : λ 2n+2 = 1}, where n ≥ 2. This family of rational maps is viewed as a singular perturbation of the bi-critical map P −n (z) = z −n if λ = 0 is small. It is proved that the Julia set J(f λ ) is either a quasicircle, a Cantor set of circles, a Sierpiński carpet or a degenerate Sierpiński carpet provided the free critical orbits of f λ are attracted by the super-attracting cycle 0 ↔ ∞. Furthermore, we prove that there exists suitable λ such that J(f λ ) is a Cantor set of circles but the dynamics of f λ on J(f λ ) is not topologically conjugate to that of any known rational maps with only one or two free critical orbits (including McMullen maps and the generalized McMullen maps). The connectivity of J(f λ ) is also proved if the free critical orbits are not attracted by the cycle 0 ↔ ∞. Finally we give an estimate of the Hausdorff dimension of the Julia set of f λ in some special cases.