编辑:正如@Jukka K. Korpela正确指出的那样，RFC 1738由RFC 3986更新。 这已经扩展和澄清了对主机有效的字符，不幸的是，它不容易复制和粘贴，但我会尽我所能。

按首先匹配的顺序排列:

host        = IP-literal / IPv4address / reg-name

IP-literal  = "[" ( IPv6address / IPvFuture  ) "]"

IPvFuture   = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )

IPv6address =         6( h16 ":" ) ls32
                  /                       "::" 5( h16 ":" ) ls32
                  / [               h16 ] "::" 4( h16 ":" ) ls32
                  / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
                  / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
                  / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
                  / [ *4( h16 ":" ) h16 ] "::"              ls32
                  / [ *5( h16 ":" ) h16 ] "::"              h16
                  / [ *6( h16 ":" ) h16 ] "::"

ls32        = ( h16 ":" h16 ) / IPv4address
                  ; least-significant 32 bits of address

h16         = 1*4HEXDIG 
               ; 16 bits of address represented in hexadecimal

IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet

dec-octet   = DIGIT                 ; 0-9
              / %x31-39 DIGIT         ; 10-99
              / "1" 2DIGIT            ; 100-199
              / "2" %x30-34 DIGIT     ; 200-249
              / "25" %x30-35          ; 250-255

reg-name    = *( unreserved / pct-encoded / sub-delims )

unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"     <---This seems like a practical shortcut, most closely resembling original answer

reserved    = gen-delims / sub-delims

gen-delims  = ":" / "/" / "?" / "#" / "[" / "]" / "@"

sub-delims  = "!" / "$" / "&" / "'" / "(" / ")"
              / "*" / "+" / "," / ";" / "="

pct-encoded = "%" HEXDIG HEXDIG

来自RFC 1738规范的原始答案:

因此，只有字母数字，特殊字符“$-_.+!*'()，”，和 可以使用用于保留目的的保留字符 没有在URL中编码。

^自1998年起过时。

URI中允许的字符要么是保留的，要么是不保留的(或者是百分比字符作为百分比编码的一部分)。

http://en.wikipedia.org/wiki/Percent-encoding#Types_of_URI_characters

说这些是RFC 3986非保留字符(第2.3节)，以及保留字符(第2.2节)，如果他们需要保留他们的特殊含义。还有一个百分比字符作为百分比编码的一部分。

RFC3986定义了两组你可以在URI中使用的字符:

Reserved Characters: :/?#[]@!$&'()*+,;= reserved = gen-delims / sub-delims gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@" sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "=" The purpose of reserved characters is to provide a set of delimiting characters that are distinguishable from other data within a URI. URIs that differ in the replacement of a reserved character with its corresponding percent-encoded octet are not equivalent. Unreserved Characters: A-Za-z0-9-_.~ unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" Characters that are allowed in a URI but do not have a reserved purpose are called unreserved.

这些都列在RFC3986中。请参阅收集的ABNF中的URI，以了解在哪里允许什么，以及用于解析/验证的正则表达式。

从这里

因此，只有字母数字，特殊字符$-_.+!*'()， 以及用于their的保留字符 保留目的可以在URL中未经编码使用。

即将到来的改变是针对中文，阿拉伯语域名，而不是uri。国际化的uri称为iri，在RFC 3987中定义。尽管如此，我还是建议不要自己这么做，而是依赖于现有的、经过测试的库，因为有很多URI编码/解码的选择，以及规范上认为安全的，以及实际使用(浏览器)上认为安全的。