TWIK-related K+ (TREK) channels are potential analgesic targets. However, selective activators for TREK with both defined action mechanism and analgesic ability for chronic pain have been lacking. Here we report C3001a, a selective activator for TREK against other two-pore domain K+ (K2P) channels. C3001a binds to the cryptic binding site formed by P1 and TM4 in TREK-1, as suggested by computational modeling and experimental analysis. Further, we identify the carboxyl group of C3001a as a structural determinant for the binding to TREK-1/2, and the key residue that defines the subtype-selectivity of C3001a. C3001a targets TREK channels in peripheral nervous system to reduce the excitability of nociceptive neurons. In neuropathic pain, C3001a alleviated spontaneous pain and cold hyperalgesia. In a mouse model of acute pancreatitis, C3001a alleviated mechanical allodynia and inflammation. Together, C3001a represents a lead compound which could advance the rational design of peripherally-acting analgesics targeting K2P channels without opioid-like adverse effects.