The invention relates to a primer pair and a probe used for noninvasive 
polygene methylation combination detection for early stage 
colorectal cancer, and includes the primer pair and the probe used for detecting 
methylation of genes Spetin9, NDRG4, BMP3, THBD and SDC2 and the primer pair and the probe for internal reference ACTB; the sequences of the primer pair and the probe are represented as the SEQ ID No.1 to the SEQ ID No.18. The invention also provides a kit containing the primer pair and the probe and applications thereof. The application method includes 
free DNA extraction from a 
plasma specimen, 
sulfite conversion, PCR amplification reaction, fluorescent 
signal detection and result determination. The kit and the method are suitable for 
methylation detection of the five genes Spetin9, THBD, SDC2, NDRG4 and BMP3 in human 
peripheral blood; compared with a conventional 
colorectal cancer diagnosis method, the application method fully utilizes the 
free DNA extraction from a 
plasma specimen, the 
DNA methylation and QPCR associated technologies, thus developing the kit having high sensitivity and specificity. The primer pair, probe and kit are used for performing early stage noninvasive screening to human 
colorectal cancer.