Spatial planning has been globally developed as a policy tool to govern built-up land expansion. However, causal evidence of the effect of spatial planning on built-up land expansion is limited, which raises doubts on the credibility of spatial planning and hinders theoretical developments in land-system science. We evaluated the effect of the Major Function Oriented Zone (MFOZ), the first strategic spatial plan in China, on built-up land expansion in Fujian Province over three time intervals (2013–2015, 2013–2018 and 2013–2020). Propensity score matching (PSM) was applied to overcome selection bias and obtain causal evidence. We implemented a conventional conformance evaluation as a reference for the PSM-based conformance evaluation, to demonstrate the problem of selection bias. The conventional conformance evaluation showed that the MFOZ effectively governed built-up land expansion in the three time intervals. The PSM-based conformance evaluation showed the smaller effect of the MFOZ and the effect was significant only in the time period 2013–2018 and 2013–2020. That is, the conventional conformance evaluation results in an initially ineffective effect of the MFOZ being estimated as effective in 2013–2015 and exaggerates the effect of the MFOZ on built-up land expansion in 2013–2018 and 2013–2020. In aggregate, Fujian’s MFOZ prevented a total of 79.31 km² of built-up land within the development-restricted zone between 2013 and 2020. To conclude, we recommend a wider application of the PSM-based conformance evaluation in evaluating the effect of spatial planning on land-use change, since this method accounts for selection bias and provides more accurate results regarding causality than conventional conformance evaluations.