The pile foundation is the most commonly used foundation for buildings in the karst area. The pile foundation construction quality problem is common due to the complexity， particularity， and irregularity of the geological conditions. The main quality problems with the pile foundation in the karst area are pile defects， local pile shaft inclination， thick settlements， and unqualified pile foundation supporting layer. The common test methods for pile foundation include the high and low strain method， ultrasonic method， and coring method. With conventional treatment， high pressure grouting is used to reinforce the pile supporting layer. In regard to a project completed in the karst area in the Longgang District of Shenzhen， an in-depth exploration of pile testing and defect treatment is conducted. The common quality problem is the defect with the pile supporting layer in the karst area. With the coring method， not only the severity and the relative location of the defect can be detected in the pile， but also presence of the karst cave， broken zone， and the weak inter-layers. High pressure jet grouting was used to strengthen the piles with defects and cement the supporting broken zone. Inspection showed that the piles can meet the original load requirement. It can provide reference for similar projects.