This paper proposes a novel method to reduce the peak-to- average power ratio (PAPR) of multicarrier signals in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems by frequency block exploitations, named cross-frequency permutation and inversion (CFPI). Our design improves the performance and framework flexibility (compatible with both space-time and space-frequency patterns) of PAPR reduction in MIMO-OFDM system, which utilizes additional degrees of frequency freedom. Especially, this proposed design can be freely combined with many good-featured space-time or space-frequency coding to achieve better whole system performance, which is unlike the previous typical methods strictly based on space-time block coding structure with relative low data rate. Simulation results show that the good performance is achieved by our novel design.