Abstract. The critical part in the development of GPS CORS network is known as the inter-station distance between the CORS or baseline length. Due to the diversity of baseline length can be implemented for the CORS network, this paper presents an alternative strategy to obtain the optimum inter-station distance between the CORS. The optimum inter-station distance between the CORS can be achieved by analysing the quality of GPS baseline data and applying GPS CORS Optimal Prediction Number Calculator (ONPC). Three baselines have been designed with appropriate range of baseline length which short (0–30km), medium (30–70km) and long (70–180km) baselines in order to examine the quality of GPS data and GPS CORS ONPC. The GPS baseline data quality analysis presents the performance of short, medium, and long baselines in term of percentage of ambiguity resolution (AR) and separated medium of GPS distance-dependent errors. The GPS CORS ONPC shows the distribution of CORS network using the length of short, medium, and long baselines within the frame and the total cost required for the establishment of the CORS network. From the result, it is found that the short and medium baselines have superior performances in term of GPS data quality which has stated higher success rate of AR (more than 50 percent) and less than 1cm standard deviation for dispersive and non-dispersive medium of GPS distance-dependent errors compared to long baseline. However, in term of cost, the longer baseline stated the cheapest, followed by medium baseline and short baseline which is 12 times and 182 times greater than longer baselines respectively. Therefore, the medium baseline is chosen as optimum inter-station distance in the development of CORS network due to better coverage and satisfied quality of GPS data with acceptable cost.