本研究旨在探討日本11～12歲男女200公尺個人混合式之分段泳姿成績做分析，利用大數據工具分析得知四式泳姿各別所隱含資訊，並以決策樹來顯示各分段成績數值意義。研究方法採用Waikato Environment for Knowledge Analysis分析軟體以C4.5演算法建構決策樹模型，資料來源是以2004～2017年日本全國青少年奧林匹克夏季及春季分齡游泳錦標賽26場次，所得成績之分析內容選取11～12歲級男子組與女子組200公尺個人混合式之項目。研究結果顯示從決策樹數據中分析男子組與女子組資料最上層之根節點皆為蝶式；從冠軍類別葉節點中發現，男子組較能奪冠泳姿為仰式及蛙式，而女子組則為蛙式及蝶式。本研究結論為男子組與女子組經分析第一優先重要泳姿皆是蝶式，表示第一趟泳姿蝶式影響成績表現最為顯著而稱其重要泳姿；其次於泳姿排序中，男子組與女子組皆擁有顯示兩條被分類為第一類別之途徑，即金牌選手類別而稱其為奪冠途徑；此外，該男子組與女子組之奪冠途徑中，皆出現蛙式的泳姿，表示第三趟蛙式影響奪冠與否扮演極具關鍵性的角色而稱其關鍵泳姿。建議應建立臺灣各賽會游泳成績之相關數據並進行分析，將數據與日本進行比較，以瞭解臺灣與日本游泳成績之差距。

This study analyzed the swimming strokes of 200 meters individual medley for Japanese swimmers aged 11-12 years (boys and girls). Big data were used to analyze four swimming strokes, and the scores for each stroke were evaluated using a decision tree. The C4.5 algorithm of the Waikato Environment for Knowledge Analysis (Weka) was used to establish the decision tree model. The results were extracted from 26 events of the Japanese Olympic Committee's Junior Olympic Cup Summer and Spring Age-Group Nationals in 2004-2017. Results of the decision tree analysis indicated that the roots of uppermost layers of men's and women's teams laid in butterfly stroke. The leaf nodes of Category 1 (champion) revealed that backstroke and breaststroke were the best stroke styles for the men's team, whereas breaststroke and butterfly stroke were the optimal styles for the women's team. This study concluded that the focused swimming style for both men's and women's teams was butterfly stroke. These findings imply that butterfly stroke in the first lap of the medley significantly affects the performance of swimmers. Regarding the medley sequence, both men's and women's teams had two paths classified as Category 1. Therefore, these paths named as ＂champion paths.＂ In addition, both paths included breaststroke, indicating that breaststroke for the third lap affected the chance of an individual champion, and it was determined as the key stroke. These findings suggest that data from various swimming events in Taiwan should be collected, analyzed, and compared with those in Japan to identify the differences in swimming performance between Taiwan and Japan swimmers.