Since plasma proteins are varied depending on diseases states, its continuous monitoring has been considered as effective diagnostic tool. In this study, a simple and efficient method for separate plasma and red blood cells (RBCs) from blood sample is proposed with a microfluidic device. To separate plasma in continuous way, microfluidic guiding channel is designed by connecting two channels with different heights in parallel, and employs inertial force and Zweifach-Fung bifurcation law. Due to its unique geometry, most RBCs flowed inside wall region with higher height. Then, plasma is collected from center region with lower height. As a result, the efficiency of plasma separation is achieved over 90 %. Furthermore, it is remained constant, even up to high value of 40% hematocrit. In the near future, the proposed method will be integrated with a lab-on-a-chip for diagnosing diseases.