As an interesting nonlinear optical effect，four-wave mixing has important applications in many fields．The magnet-free optical non-reciprocity is realized by using the four-wave mixing effect．The effects of signal optical detuning，pump optical power and gas pool temperature on the transmittance of signal light during forward and backward propagation are investigated．The experimental results show that the forward transmittance can be controlled effectively by changing these parameters，while the very low reverse transmittance is almost unaffected．It has a certain reference value for college physics experiment teaching．