The invention relates to a position speed controllable quasi-optimal explicit guidance method in a power decrease process; the quasi-optimal explicit guidance method respectively use the maximum thrust and minimum thrust as input values, and uses a normal thrust power explicit guidance method to calculate guidance parameters and predict terminal positions corresponding to the thrusts; according to a relation between a target position and predicted terminal positions under two different thrusts, the quasi-optimal explicit guidance method can automatically determine whether to use the maximum thrust or the minimum thrust to guide, thus realizing automatic switching between the maximum trust and minimum thrust. The invention only relates to two PEG guidance rules for calculation, and the computational complexity is smaller when compared with an iteration thrust adjusting mode; the thrust control uses an automatic maximum-minimum switching mode, an engine usage efficiency is higher than continuous variable thrusts, so propellant consumption is theoretically least.