CREATE PROCEDURE transpro
  @aid1 FLOAT,
  @aid2 FLOAT,
  @num  INT
AS
BEGIN
  DECLARE @ye INT
  DECLARE @error INT

  BEGIN TRANSACTION

  SELECT
    @ye = jine
  FROM   account
  WHERE
    aid = @aid1

  IF(@num > @ye)
  BEGIN
    PRINT '卡上余额不足'

    ROLLBACK TRANSACTION
  END
  ELSE
    UPDATE account
    SET    jine = jine + @num
    WHERE  aid = @aid2

  SET @error=@error + @@error

  UPDATE account
  SET    jine = jine - @num
  WHERE  aid = @aid1

  SET @error=@error + @@error

  IF @error > 0
  BEGIN
    PRINT '转账失败！'

    ROLLBACK TRANSACTION
  END
  ELSE
  BEGIN
    PRINT '转账成功！'

    COMMIT TRANSACTION
  END
END

------解决方案--------------------
余额足够才进行转账，看你的代码觉得Else和最后一个End之间的代码是@num <= @ye时才执行的，因此要在Else和最后一个End之间加上Begin...End。

SQL code

CREATE PROCEDURE transpro
  @aid1 FLOAT,
  @aid2 FLOAT,
  @num  INT
AS
BEGIN
  DECLARE @ye INT
  DECLARE @error INT

  BEGIN TRANSACTION

  SELECT
    @ye = jine
  FROM   account
  WHERE
    aid = @aid1

  IF(@num > @ye)
  BEGIN
    PRINT '卡上余额不足'

    ROLLBACK TRANSACTION
  END
  ELSE
  BEGIN
    UPDATE account
    SET    jine = jine + @num
    WHERE  aid = @aid2

    SET @error=@error + @@error

    UPDATE account
    SET    jine = jine - @num
    WHERE  aid = @aid1

    SET @error=@error + @@error

    IF @error > 0
    BEGIN
      PRINT '转账失败！'

      ROLLBACK TRANSACTION
    END
    ELSE
    BEGIN
      PRINT '转账成功！'

      COMMIT TRANSACTION
    END
  END
END

------解决方案--------------------
if /else 如果没有加begin /end 的话，默认只执行最接近这个关键字的那句操作，所以建议楼主要规范化编程。不然会有很多后续问题浪费你时间