The invention relates to an opened type lubricating oil groove for a machine tool sliding guide rail. The opened type lubricating oil groove is composed of an oil inlet section, a lubricating section and an ending section and is characterized in that the oil inlet section and the lubricating section are of an oil groove structure deeper and wider than the ending section; and the tail end of the ending section is communicated with the outside. According to the opened type lubricating oil groove for the machine tool sliding guide rail, the oil groove with the wide and deep front portion and the narrow and shallow rear portion is arranged so that the oil groove can have certain storage space, a concentrated quantitative lubricating device is utilized, the oil supply amount each time is quantitative and the same, lubricating oil is fully utilized, waste is reduced, pollution is reduced, production cost is reduced, and moistening is effectively improved.