This paper proposes an improved finite control set model predictive control (FCS-MPC) algorithm based on virtual space vector to reduce computational burden, and achieve a constant switching frequency for two-level three-phase inverters. The voltage vector reference is calculated in a 60° coordinate system according to the principle of deadbeat (DB) technique. A large number of virtual voltage vectors synthesized by discrete space vector modulation (DSVM) is utilized to approach the voltage vector reference. To avoid enumerating all the virtual voltage vectors from a look-up table, an algebraic way using the voltage vector reference is adopted to calculate the three candidate vectors. Then, a cost function is defined to select the optimal voltage vector among them. This new method greatly improves the computation efficiency since plenty of multiply operation is eliminated in the 60° coordinate system. Moreover, a fixed switching frequency is achieved since the durations of each switch states has been calculated. Experimental results under a two-level three-phase inverter verify the effectiveness of the proposed control strategy.