To develop a novel composite gel with whey protein isolate (WPI) and potato protein hydrolysate (PPH), their mixtures were pretreated using ultrasound and transglutaminase (TGase) before gel formation. The effects of ultrasound and TGase pretreatments on the properties of the composite gel were assessed using a texture analyzer, rheometer, low-field nuclear magnetic resonance (LF-NMR), and scanning electron microscopy (SEM). The results show that the hardness, gumminess, resilience and chewiness of gel samples pretreated using ultrasound and TGase were lower than those of the control samples (P<0.05), but were higher than those of the gel samples treated with TGase only (P<0.05). For the ultrasound and TGase pretreated composite gel, increasing the ultrasonic pretreatment time enhanced the final storage and loss moduli of the gel at the end of the heating and cooling cycles in the rheometer. The swelling ratio of the gel samples that underwent 15- and 30-minute ultrasonic and TGase pretreatments increase by 11.55% and 55.02%, respectively, compared with that of the gel samples with only TGase pretreatments. Simultaneously, the free water content increased by 62.22% and 111.11%, respectively. The SEM images of gels with ultrasound pretreatments only demonstrate larger protein aggregates, and a dense network with low uniformity in its microstructure. Contrarily, the gels with ultrasound and TGase pretreatments exhibited small protein aggregates, and a compact and homogeneous microstructure network. In conclusion, the combination of ultrasound and TGase pretreatments significantly affects the microstructures and properties of WPI and PPH composite gels. The findings facilitate the development of novel protein gels and provide a reference for adjusting the properties of composite gels.