Abstract: Lowering the liquid level in tundish in the mixed casting of different steel grades is adopted to reduce the intermixed slab length but the increase of inclusions in slab arises, however non-lowering the liquid level in tundish is applied to implement steady-state operation and increase the intermixed slab length. Non-lowering the liquid level in tundish was applied in the mixed casting mixed casting of the SPHC and DC01 in a steel factory, the cleanness of the intermixed slab and the influence of it on mechanical properties of steel plate were comprehensively evaluated by optical microscope, scanning electron microscope analysis, Sample-electrolyzing method and multi-use mechanical testing machine. The results showed that content difference of total oxygen between intermixed slab and normal slab was 10×10^-6 to 15×10^-6, nitrogen content maintained about 70×10^-6. Distribution density difference of inclusions was 8.54 to 8.89 per/mm², content difference of large inclusions was 2.6 mg/10 kg, morphology and type of large and micro inclusions were basically consistent. tensile strength, yield strength, elongation after fracture of corresponding steel plate of the intermixed slab was more 11 MPa,32 MPa and 5.7% than that of normal slab in turn. Therefore, the intermixed slab and corresponding steel plate generated by non-lowering the liquid level in tundish should be degraded to reduce the rejection rate.