It is an object of the present invention to provide a method for determining a pattern for modulating the power of a laser beam which can determine a pattern for modulating the power of a laser beam so that data can be recorded in a write-once type optical recording medium with a laser beam having a low recording power at a high linear recording velocity. The method for determining a pattern for modulating the power of a laser beam according to the present invention includes the steps of determining pulse train patterns by fixing a recording power at a predetermined level and varying the level of a bottom power, modulating the power of the laser beam in accordance with the pulse train patterns to record first test signals in the optical recording medium, reproducing the first test signals, determining the optimum level of the bottom power based on the amplitude of the thus reproduced first test signals, determining pulse train patterns by fixing the bottom power at the optimum level and varying the level of the recording power, modulating the power of the laser beam in accordance with the pulse train patterns to record second test signals in the optical recording medium, reproducing the second test signals and determining the optimum level of the recording power based on at least one of jitter and error rates of the thus reproduced second test signals.