The methods for cell evaluation can be categorized into two groups, which are indirect methods and direct methods. The indirect methods, such as microfluidics, become popular recently, and based on the nature of evaluation approach, indirect method can be further grouped into active and passive evaluation. Active evaluation is to actively manipulate cells in a microchannel by feedback controls cell position. In this work, we focus on the active evaluation system of indirect method, and aim to realize the true transfer function of the system. The challenging point is that the performance of active system usually involves feedback function in the overall transfer function, so the true transfer function cannot be easily observed. To solve the problem, we apply a direct control to the actuator in an open-loop control, and determine the true transfer function from the input and output directly.