正则替换

var kstr = "http://www.abc.com/images/2013/538/794/321497835_5554335435_{任意数字}x{任意数字}.jpg";

// 要求转成

kstr = "http://www.abc.com/images/2013/538/794/321497835_5554335435.jpg"

[解决办法]
var k = "http://www.abc.com/images/2013/538/794/321497835_5554335435_{1212}x{12113}.jpg";
k=k.replace(/_\{\d+\}x\{\d+\}/,'');
alert(k);