Son-yu represented her nation at international competitions. As a junior she participated at the World Junior Speed Skating Championships. At elite level she competed at the ISU Speed Skating World Cup during the 1989–90 season in November 1989 in the 500 metres event in Berlin, Germany. She competed at the 1990 Asian Winter Games in the 500 metres event (finishing 9th) and 1000 metres event (finishing 10th). She also competed at other international competitions.