是的，看看 combine_first 或更新。例如：

>>> df1['val'] = df2['val'].combine_first(df1['val'])
>>> df1
Out[26]:
    c1  c2  val
0    a   x   12
1    a   y   31
2    b   x   14
3    b   y   0

编辑：根据c1和c2结合忽略当前索引：

to combine according to c1 and c2 ignoring the current index:

>>> df1['val'] = df2.set_index(['c1','c2'])['val'].combine_first(df1.set_index(['c1','c2'])['val']).values
>> df1
Out[25]:
    c1  c2  val
0    a   x   12
1    a   y   31
2    b   x   0
3    b   y   14