One of the main problems of finite control set model predictive control (FCS- MPC) is that the switching frequency is not fixed, which leads to switching loss, current resonance, electromagnetic interference and so on. An improved FCS-MPC strategy based on periodic control is proposed for 3L- NPC inverters. On the basis of ensuring the original load current tracking and neutral capacitor voltage balance control objectives, the control objectives of fixed switching period change are realized. The appropriate weighting factors are determined by artificial statistics, and different reference switching frequencies and reference currents are tracked by simulation to verify the feasibility of the algorithm.