This paper reports a microfluidic labonchip device which can automatically and sequentially realize the impurity dielectrophoresis separation and resistance pulse detection, counting, and sizing of the target particles. According to the differences of the size and dielectric properties of the impurity and target particles, and the dielectrophoresis (DEP) separation and resistive pulse detection (RPS) zones in the channel are sequencially design. By theoretical simulation, the structure and size of the chip are optimized and defined. Also, the separation of 3μm polystyrene particles and detection and counting of the Pseudokirchneriella subcapitata are experimentally achieved. Results show that the position of the particle collection channel arrangement has an important influence on particle collection. In addition, the S/N of the detection of Pseudokirchneriella subcapitata is higher, which means high voltage does not impact the S/N. This research has some value for the development of fast detection and analysis techonologies of the microfluidic chipbased portable devices for the single cell organism detection within complex samples.