我认为您需要首先转换两列，
to_datetime因为需要相同的内容
dtypes：
df1.month = pd.to_datetime(df1.month)df2.month = pd.to_datetime(df2.month)print (pd.merge(df2, df1, how='outer', on='month')) factor monthamt0 1.000000 2015-02-01 1.549368e+061 1.000000 2015-03-01 2.175802e+062 1.000000 2015-04-01 1.915613e+063 1.000000 2015-05-01 1.703064e+064 0.998897 2015-06-01 1.770041e+06
#convert to str date columndf2.month = df2.month.astype(str)print (pd.merge(df2, df1, how='outer', on='month')) factor monthamt0 1.000000 2015-02-01 1.549368e+061 1.000000 2015-03-01 2.175802e+062 1.000000 2015-04-01 1.915613e+063 1.000000 2015-05-01 1.703064e+064 0.998897 2015-06-01 1.770041e+06
