In MIMO full duplex system,power amplifier(PA) nonlinearity limits the self-interference(SI) cancellation seriously. Most existing methods need to model and estimate the PA nonlinearity in order to reconstruct the SI,however the estimation error caused by the mismatch between the estimated PA model and the actual PA property still impacts the cancellation ability,especially when the transmit power is high. In this paper we propose a polarization oblique projection based self-interference cancellation method which does not need to estimate the PA nonlinearity coefficients. It exploits the polarization state information of the signals which is immune to the PA nonlinearity,and establishes an oblique projection operator to cancel the SI. Numerical results and analysis demonstrate that it can cancel the nonlinear SI effectively. Moreover the signal to interfere plus noise ratio(SINR) and the achievable sum rate do not deteriorate when the transmit power is high. Further,the upper bound of the achievable sum rate can be more than twice that of the half duplex. In MIMO full duplex system, power amplifier (PA) nonlinearity limits the self-interference (SI) cancellation seriously. Most existing methods need to model and estimate the PA nonlinearity in order to reconstruct the SI, however the estimation error caused by the mismatch between the estimated PA model and the actual PA property still impacts the cancellation ability, especially when the transmit power is high. In this paper we propose a polarization oblique projection based self-interference cancellation method which does not need to estimate the PA nonlinearity coefficients. It exploits the polarization state information of the signals which is immune to the PA nonlinearity, and establishes an oblique projection operator to cancel the SI. SINR) and the achievable sum rate do not deteriorate when the transmit power is high the achievable sum rate can be more than twice that of the half duplex