Herein, a cell segmentation model is proposed based on the U-Net and combination of residual block and attention mechanism. This model aims at addressing the problems of uneven brightness and low contrast between a cell and background of cell images collected using a phase contrast microscope. First, the U-Net with encoder-decoder structure is used to conduct the initial segmentation on cell images. Hereafter, the residual block is introduced into the U-Net to strengthen the propagation ability of the features and extract more cell-detail information. Finally, the attention mechanism is used to increase the weight of the cell area and reduce the interference of uneven brightness and low contrast on the model. The experimental results show that compared with other models, the proposed model exhibit better segmentation results in visual effects and objective evaluation indicators.