function keyPress(){
	var keyCode = event.keyCode;
	if(keyCode>=48 && keyCode <= 57){
		event.returnValue=true;
	}else{
		event.returnValue=false;
	}
}

function formSubmit(){
	var min = parseInt($("#id1").val());
	var max = parseInt($("#id2").val());
	if( min > max ){
		$("#errorId").html("开始值必须小于结束值");
		return false;
	}else{
		return true;
	}
}

?上面是JS代码

下面是HTML代码

<form action="#" onsubmit="return formSubmit()">
<input type="text" name="minNum" id="id1" onkeypress="keyPress()">
<input type="text" name="maxNum" id="id2" onkeypress="keyPress()">
<input type="submit">
<span id="errorId"></span>
</form>