This paper is based on the study of a four-cylinder direct-injection compression ignition (DICI) engine, maintaining the engine speed at 1800 rpm and selecting the five load points of 0.13, 0.38, 0.63, 0.88, and 1.13 MPa BMEP. Pure soybean biodiesel and tetrahydrofuran (THF)-biodiesel mixtures with blending ratios of 10, 20, and 30% were burned under each load. The combustion and emission characteristics of different fuels were compared and analyzed. We found that the combustion of BT30 was poor and its emissions were high under low loads. Compared with other fuels, the P-max, HRRmax, and PRRmax of BT30 were obviously attenuated. At 0.13 MPa, the ignition delay (ID) and combustion duration (CD) of BT30 were significantly prolonged, and various emissions were at a high level. The emission of CO, HC, soot, 1, 3-butadiene, and acetaldehyde increased by 27.2, 5.6, 140, 18.3, and 14.5%, respectively, compared with biodiesel. In other cases, with the increase of THF blending ratio, the ID was prolonged and the CD was shortened, which meant that the combustion was more compact. The P-max, HRRmax, and PRRmax showed an upward trend generally, and all emissions other than NOX were reduced. In addition, THF increased the brake-specific fuel consumption and decreased the brake thermal efficiency of the mixed fuel slightly.