其他的答案都含有显著遗漏。

The other answers all contain significant omissions.

的是运营商做的不的检查操作数的运行时类型的究竟的给定类型;相反，它检查是否运行时类型的与的给定类型兼容：

The is operator does not check if the runtime type of the operand is exactly the given type; rather, it checks to see if the runtime type is compatible with the given type:

class Animal {}
class Tiger : Animal {}
...
object x = new Tiger();
bool b1 = x is Tiger; // true
bool b2 = x is Animal; // true also! Every tiger is an animal.

但检查类型的标识的与反思检查的标识的，不是的兼容性的

But checking for type identity with reflection checks for identity, not for compatibility

bool b3 = x.GetType() == typeof(Tiger); // true
bool b4 = x.GetType() == typeof(Animal); // false! even though x is an animal

如果这不是你想要的，那么你可能想IsAssignableFrom：

If that's not what you want, then you probably want IsAssignableFrom:

bool b5 = typeof(Tiger).IsAssignableFrom(x.GetType()); // true
bool b6 = typeof(Animal).IsAssignableFrom(x.GetType()); // true! A variable of type Animal may be assigned a Tiger.