我們利用2MASS資料庫,分析星團的空間結構。2MASS的極限星等對大多數的球狀星團而言,並不夠深,僅供分析後主序星的分佈情形。但卻相當適合於距離較近,較年輕的疏散星團。我們發現不論是極年輕(數百萬年)或極年老的(數十億年),其成員星皆有向星團中心集中分佈的趨勢。對年輕星團而言,反映了原始分子雲在收縮,形成恆星時的情形。理論上當星團的年齡大於其鬆弛時間之後,成員星會產生質量分層效應,我們在中年齡的星團看到了這樣的情形,此亦反映出星團內部動力演化之結果。在年老星團中,並未出現此效應,原因很有可能是環境造成的影響,例如銀河盤面的潮汐力,差分自轉,都會破壞、扯裂其結構。 We present results of a pilot program to study star clusters with the 2MASS database. While 2MASS cannot resolve the cores or detect much of the main sequence of globular clusters, the homogeneity and large angular coverage make the database suitable to study young star clusters. We show that very young star clusters have their stars --- regardless of their masses --- concentrated progressively toward the center, a result more from the formation process of the cluster than from subsequent stellar gravitational interaction. We show evidence of mass segregation, and effects of external disturbances on evolution of the spatial structure of many young star clusters.