Pore defects have a significant impact on the performance and reliability of SLM (selective laser melting) formed parts. The previous pore evolution research is separately carried out from two aspects: the monitoring of the forming process and the analysis of the forming results. In this paper, a new method for studying the evolution of SLM pores with layer thickness driven by the fusion of forming process monitoring and forming result detection was proposed. By obtaining visible light monitoring images of GH4169 alloy SLM forming solidification and CT detection images of SLM formed parts, specific areas of a pore were selected and the feature parameters were extracted. Then, the changes in pore feature parameters with layer thickness in both images were characterized and analysed. The results show that the variation of pore characteristic parameters in CT images with layer thickness lags behind that in visible light images. In the first half of pore formation, the formation of the N+1 layer has a shrinking effect on the pores of the N(or below) layer, and the latter half has an expanding effect. The formation of the N+1 layer has the effect of reducing the roundness of the pores in the N (or below) layer. Since only specific pores have been studied, the conclusions need to be further verified. But this work provides a new way to study the evolution of SLM forming defects with layer thickness, which will be further studied in the future.