To investigate the effect of soy protein isolate on the quality of whole-grain flat rice noodles, the texture as well as the cooking properties and flavor of flat rice noodles, whole-grain flat rice noodles and whole-grain flat rice noodles with soy protein isolate were investigated. Among the three tested rice noodles, whole-grain flat rice noodles with soy protein isolate showed the highest cohesiveness, adhesiveness, resilience, and springiness. Compared to the flat rice noodles and whole-grain flat rice noodles, whole-grain flat rice noodles with soy protein isolate increased their moisture content and water absorption, whereas the opposite trend was observed for their cooking loss. The electronic nose analysis showed stronger response values at W5S, W1W, and W2W. Solid phase micro extraction and gas chromatography–mass spectrometry results showed that aldehydes are the main volatile compounds in whole-grain flat rice noodles and whole-grain flat rice noodles with soy protein isolate. Moreover, seven more volatile compounds were detected in whole-grain flat rice noodles with soy protein isolate compared to flat rice noodles and whole-grain flat rice noodles. The whole-grain flat noodles with the addition of SPI are more sensory acceptable. Thus, soy protein isolate, as a natural and safe additive, could be used to improve the quality and enrich the flavor of whole-grain flat rice noodles.