Orifice flow meter constitutes one of the most common differential pressure flow meters. However, high energy loss is occurred with the measurement process. The present research considers 3𝐷 steady simulation using Reynolds Averaged Navier–Stokes equations (RANS). New design of the orifice plate s carried out using the adjoint method. Optimal shape of orifice plate shows 55 % reduction of the pressure loss coefficient at a Reynolds number 𝑅𝑒=1.84 × 104. The discharge coefficient 𝐶𝑑 is increased by 39 %. Also, the effect of downstream ring is investigated. Optimize the shape of the ring has a slight effect on reducing energy consumed. However, applying adjoint method on the orifice plate with downstream ring achieves considerable effect in the pressure loss. Reduction by 34 % in pressure loss coefficient is obtained by the optimal orifice with downstream ring. Shape optimization by the adjoint method has a significant contribution in decreasing the consumed energy through the orifice meter.