Wireless sensing technologies have exploited various methods for contactless respiration monitoring. One of the main methods is to use an acoustic beam to cover the chest and abdomen with real-time and high-resolution ranging. The system with high ranging resolution can detect small distance transformations, further affecting the precision of respiratory monitoring. However, the traditional range-based respiration monitoring systems are limited by an insufficient sampling rate and poor synchronization. The ranging resolution is between millimeters and centimeters. In this study, we introduced a novel, high-precision ultrasound-based system for contactless respiration monitoring. First, we developed a convenient and high-performance ultrasonic transceiver platform with universal serial bus audio architecture to eliminate the above limitations. The developed platform provides a foundation for acoustic sensing. Furthermore, based on this platform, we designed a cross correlation sine-frequency modulation continuous wave ranging method and a real-time respiration wave recovery method. The median error in monitoring respiration for 12 participants in three different sleep postures is 0 breaths/min, and the maximum error is 0.58 breaths/min. The proposed system has strong robustness concerning different respiration rates, long-term continuous respiration monitoring, and simulated apnea.