A technique facilitates controlled injection of a chemical injection fluid at a desired downhole location. A chemical injection valve is mounted along a well tubing and is disposed externally of an internal flow passage through the well tubing. The chemical injection valve is operated via hydraulic pressure which is applied to actuate the chemical injection valve between closed flow and open flow positions. The chemical injection valve controls flow of the chemical injection fluid to at least one injection port. The at least one injection port may be positioned to inject the chemical injection fluid into the internal flow passage of the well tubing.