Pressure drops of flow boiling in a single microchannel having low aspect ratio were studied with effects of the inlet temperature，mass flux，heat flux and the inclined angle using methanol as working fluid. The present experimental data were compared with the predictions of the homogeneous flow model and separated flow model respectively. The comparison indicates that the homogeneous flow model cannot predict the twophase pressure drop well except using the twophase viscosity model of the Dukler correlation. With the existing correlations for parameter C in LockhartMartinelli correlation such as Chisholm,Lee and Lee,Mishima,Qu and Mudawar , separated flow model also failed to predict the twophase pressure drop in the microchannel of this study . The experimental data in this work show that the interaction between vapor phase and liquid phase is decreased with the increasing quality when the quality reach a certain value , accordingly there needs a correlation for C which decreased with the decreasing mass flux .A new correlation to predict the twophase flow pressure drop in microchannels was developed in the form of the LockhartMartinelli correlation .It includes the effect of the hydraulic diameter and the effect of mass flux on the twophase flow pressure drop in microchannels .The new correlation developed in this study predicted the experimental data within a mean absolute error of 16.9%.