Abstract: Lambert's problem is studied for spacecraft rendezvous.Main geometrical properties of transfer orbit are interpreted.The Lagrange equation for transfer time was used to analyze the relationship between the transfer-time and orbital parameters.A graph method was presented to find the optimal transfer revolution;and the minimum-Δv,fixed-time,two-impulse rendezvous(between) two spacecraft orbiting along two coplanar unidirectional circular orbits were studied.For a given rendezvous time and an initial separation angle,optimal initial and termingal coasting periods can be found via a comparing-one-by-one method to obtain the globally minimum-Δv.