This paper describes the improved quasistatic method for solving reactor transient equations in three-dimensional region.Two transient problems are calculated, and results are compared with these by traditional direct numerical difference methods.For TWIGL problem the maximum error of power is 1.57%, for CANDU reactor model, near maximum power point, the maximum error of thermal neutron flux is 0.88% in comparing with the reference solution, hence the results are satisfactory the advantage of saving computation is demonstrated.