The present invention relates to a method for detection of ink residual, an ink residual detection mechanism, an ink supply system and an ink jet printer. The method is configured to detection whether there is ink or not. The method comprises the following steps: 1, setting a presetting value having larger suction power than the normal suction power; 2, detecting whether the position has ink or not through an ink residual detection part, and if the position has no ink, entering the step 3; 3, comparing the real-time suction power to the presetting value, if the real-time suction power is smaller than the presetting value, performing the step 4, and on the contrary, turning the step 5; 4, adding the suction power, and entering the step 2; and 5, prompting that the ink is exhausted. After the ink residual detection part detects that the position has no ink, and the suction power of an ink suction needle is increased to allow the ink remained in an ink box to be pumped out until the power to be sucked reaches the presetting value and the ink residual detection part detects that the position has no ink, the printer prompts that the ink is exhausted. The method for detection of ink residual, the ink residual detection mechanism, the ink supply system and the ink jet printer can accurately detect the ink residual in the ink box to allow the ink residual in the ink box to reach the minimum and avoid the damaging caused by the air suction of the ink suction needle.