The problem of a hydrogen atom in a strong magnetic field is solved quantum-mechanically in the (r,ρ,φ) coordinate system.The main part of the Hamillonian can be solved by separation variables and the remaining part is small and is treated as a perturbation,The zeroth order energy and wave function are obtained, the expression for the first perturbation energy is derived, the well-known quasi-Landau resonance interval 3/2h ω_C near thresold and the approximate scaling law ³γ≈1 are dediced amd the approximate dynamical symmetry possessed by this system is found.