The traditional facilities that used to find range are mostly based on laser or ultrasonic. Now, based on binocular parallax of human eyes, we advance a method used to get the distance by measuring the offset on image panel. On this foundation, we also analyze the error in forward. The academic analysis indicate that the measurement would be impacted severely by transverse offset and angle-measuring offset, in contrast, much slightly by lengthways offset. When we put this facility into practice, this facility can suffice practical demand completely if we select the space between bi-camera and the focus of facility rationally.