不要设置输入类型在您的标记或呈现前ASP.NET将清除输入。相反，使用以下标记：

Don't set the input type in your markup or ASP.NET will clear the input before it is rendered. Instead, use the following markup:

<input id="tbPassword" name="password" runat="server" />

...及以下code在code-背后：

...and the following code in your code-behind:

tbPassword.Value = "your password";
tbPassword.Attributes["type"] = "password";

不过，我强烈反对这种做法。其一，你不应该采用明文存储密码。这是一个非常糟糕的安全做法。

However, I strongly advise against this approach. For one, you shouldn't be storing passwords in plain text. It's a really bad security practice.

二，如果你只是要设置code中的密码，为什么需要它呢？一个密码输入的点是为用户交互（输入密码）。如果你这样做对他们来说，然后有在页面上是没有意义的。

Two, if you're just going to set the password in code, why require it at all? The point of a password input is for user interaction (entering a password). If you do that for them, then having it on the page is pointless.