The objective of this paper is to upgrade a wireless sensing unit which can meet the following requirements: 1) Improvement of system powering and analog signal processing 2) Enhancement of signal resolution and provide reliable wireless communication data, 3) Enhance capability for continuous long-term monitoring. Based on the prototype of the wireless sensing unit developed by Prof. Lynch at the Stanford University, the following upgrading steps are summarized: 1. Reduce system noise by using SMD passive elements and preventing the coupling digital and analog circuits, and increasing the capacity of power. 2. Improve the ADC sampling resolution and accuracy with a higher resolution Analog-to-Digital Converter (ADC): a 24bits ADC with programmable gain amplifier. 3. Improve wireless communication by using the wireless radio 9XTend which supported by the router (Digi MESH) communication function using 900MHz frequency band. Based on the upgrade wireless sensing unit, verification of the new wireless sensing unit was conducted from the ambient vibration survey of a base-isolated building. This new upgrade wireless sensing unit can provide more reliable data for continuous structural health monitoring. Incorporated with the identification software (modified stochastic subspace identification method) the smart sensing system for SHM is developed.