We present a microfluidic chip where droplets of different liquids and sizes can be generated and merged independent of the droplets size and inter-droplet separation. The designed chip consists of two T-junctions located at each side of the long channel and a droplet merging area located at the center of the channel. Our system uses an extra outlet placed before the merging area, which allow the control of the travel time, hitting speed, and merging location of the droplets. From one side of the channel droplets can be generated and stored for several hours. At the other side of the channel droplets containing reagents can be made. Individual droplets generated at each side of the channel can be selected, transferred to the centre location of the channel, and merged with each other. Due to simplicity and efficiency of this droplet merging method, the system can be easily used for on-chip cell analysis.