There exist some problems such as flow instability and critical heat flux (CHF) caused by the local dryout phenomenon, which is an obstacle to the application of microchannel flow boiling heat sink. Utilizing self-rewetting fluid is one of the promising ways to minimize the dryout area, thus increasing the heat transfer coefficient and CHF. To investigate the heat transfer performance of self-rewetting fluid in microchannel flow boiling, a numerical investigation is carried out in this study using the volume of fluid (VOF) method, phase-change model, and continuum surface force model with surface tension versus temperature. A three-dimensional numerical investigation of bubble growth and merger is carried out with water and 0.2 wt % heptanol solution. The single bubble growing cases, two x-direction/y-direction bubbles' merging cases, and three bubbles' merging cases are conducted. Since the bubbles never detach the heated walls, the dryout area and regions nearby the contact line with thin liquid film dominated the heat transfer process during the bubbles' growth and merger. The self-rewetting fluid can minimize the local dryout area and achieve larger thin liquid film area around the contact line due to the Marangoni effect and thermocapillary force, thus resulting in higher wall heat flux. The two x-direction bubbles' merging case performed best for heat transfer in the microchannel, in which self-rewetting fluid achieves heat transfer enhancement for over 50%.