Instant wireless sensor network (IWSN) is a type of WSN deployed for a class of special applications which have the common requirement on instantly responding for collecting and transmitting sensory data, e.g., volcanic eruption monitoring or nuclear leakage detection. In this paper, having a clusterbased WSN, we present a compensation-based reliable data delivery protocol (CRDD) to collect and transmit sensory data timely, reliably, and energy-efficiently. The CRDD consists of three important parts: 1) reliability calculating mechanism, 2) information classifying mechanism, and 3) intelligent balancing mechanism. By using these three mechanisms, the CRDD can reduce redundant messages for enhancing the transmission performance and compensate the deficient messages for reliability. The simulation results show that CRDD can outperform both LEACH and ECDG and significantly improve sensory data collection speed and system dependability.