Detent force of a permanent magnet linear motor(PMLSM) consist of cogging and drag forces, and should be minimized for high precision control purpose applications. This paper shows that the cogging force can be reduced effectively by employing 9 pole 10 slot structure. The drag force is minimized by optimizing the total length and shape of the exterior teeth of armature core simultaneously by using($1+{lambda}$) evolution strategy coupled with response surface method. After optimization, the optimized PMLSM is proven to reduce 95% and 92.6% of the cogging and total detent forces, respectively, and give 12% and 6.4% higher Back-emf and thrust force, respectively, compared with a conventional 12 pole 9 slot structure under the same condition. Additionally, Simulation results by the proposed optimum design are verified by the experiment results.