Ultrasonic sensor is being used widely for its simplicity and cheap cost. It can measure the distance to objects just measuring the time of flight of the ultrasound. Inspired by studies about the bat's echolocation system, we tested the cross-correlation of FM ultrasonic signals and its possibility for the echolocation system. In this paper we simulate object discrimination experiments which are supposed to distinguish a prey object from the background objects with ultrasonic signals. We assume a prey object is located in the cluttered environment. The cross-correlation between the transmitted signal and the echoed signal produces an impulse-like signal for objects in the environment. The simulation result suggests that the prey object can be discriminated from the cluttered background better with a higher sweep rate of FM ultrasonic signals.