The high order harmonic generations (HHG) of three-dimensional hydrogen atom which exposed to the combination of two laser pulses were studied. When the combined field has a proper frequency ratio of 3:5, and the relative intensity of the additional laser field reaches a specific value (0.35), the single short pulse can be obtained directly. A new method to obtain the single short pulse is proposed, the main points of the method are the following. Frequency ratio of the two lasers should be adjacent odd, and the relative intensity of the additional laser to basic laser should fall on a particular value. In future research, the atoms with a higher binding energy can be chosen, and the width of HHG’s plateau will be enlarged, so the width of pulse will be reduced.