The invention discloses a straightness error compensation method using laser direct feedback; the method comprises the following steps: reading a linear motion position I of the present machine tool detected by a laser interferometer; recording a linear motion position II, outputted by a machine tool motion control system displacement sensor, in the same time; meanwhile calculating and recording the difference value between the laser interferometer motion position and encoder detected linear motion positions I and II; repeating said steps, and summing obtained difference values at each moment to serve as whole system error compensation; carrying out error compensation for the motion control system. Compared with the conventional linear error compensation mode, the straightness error compensation method can greatly improve linear position compensation efficiency, and thus greatly improving linear compensation precision; the straightness error compensation method employs mature technology, is simple in structure, and very suitable for being applied to and promoted in large scale in the precision numerical control machine tool field.