【Purposes】 Diseases such as hypertension and malaria infection often raise the rigidity of red blood cells (RBCs). Consequently, the morphology and rheological characteristics of RBCs change, which means understanding the deformability and flow characteristics of sick RBCs is of great significance for clinical diagnosis and drug treatment. 【Methods】 In this work, RBCs were treated with a series of fixatives to mimic sick RBCs. Devices such as microfluidic chip, injection pump, fluorescence inverted microscope, and high-speed camera were used to study the flow characteristics of treated RBCs flowing in microchannel in vitro. The relationships between the deformability of RBCs and Cell free Layer (CFL) thickness, flow velocity, and other parameters were explored. 【Findings】 The results show that, after treating with fixative solution, the diameter of RBCs increases, the width of CFL becomes thinner, and the velocity of RBCs becomes lower. After the disease, the rigidity of RBCs is enhanced, the deformability is reduced, and the flow characteristics of red blood cells are obviously changed.