The dispersion relation for weak relativistic inhomogeneous plasma in general magnetic field configurations is derived from the relativistic gyrokinetic equations, which is valid for arbitrary frequencies. In the derivations the singular integrations with the quadratic denominator are represented by the drift plasma dispertion functions. This dispersion relation can be used to study the various micro instabilities driven by gradient and curvature of B, weak relativistic effects, and/or gyrofrequency shift. Extending the results to the nonequilibrium case such as loss-cone distribution is simple and straight forward. For demonstration, we apply it to investigate the lower hybrid drift instability. Using this dispersion relation we can recover the re-suits of Drake et al. in a straight forward and much more transparent way.