In order to clarify the effects of decomposed maize straw liquid on F. pseudograminearum, the growth rate method and coating plate method were used to determine the effect of corn straw decomposition solution on mycelial growth and spore germination of F. pseudograminearum. The activities of PG and PMG were determined by DNS method, and the activities of PGTE and PMTE were determined by Hoffman method. The results showed that 0, 7 and 14 days after decomposition of corn straw had low promoting and high inhibiting effects on mycelial growth and spore germination, and the treatments with the concentration higher than 0.062 5 g·DW/mL had inhibitory effects,and the inhibitory effect became stronger with the increase of decomposition days, with the highest inhibition rates of 100% and 93.7%, respectively. The decomposed maize straw liquid showed an inhibition on activities of PMTE and PGTE of F. pseudograminearum, and the inhibition rates were between 1.2% to 99.0% and 6.6% to 99.6%, respectively. The results showed that PG activity increased by 4.2%～22.2% and PMG activity increased by 2.3%～10.7% in the range of 8.787～10.420 U/mg and 7.557～8.177 U/mg, respectively, compared with the control, when the decomposition solution concentration was lower than 0.062 5 g·DW/mL for 7 and 14 days. This study reveals the causes of repeated occurrence of wheat crown rot under the condition of straw returning to field.