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In the production of astaxanthin from <i>Haematococcus pluvialis</i>, the process of growing algal biomass in the vegetative green stage is an indispensable step in both suspended and immobilized cultivations. The green algal biomass is usually cultured in a suspension under a low light intensity. However, for astaxanthin accumulation, the microalgae need to be centrifuged and transferred to a new medium or culture system, a significant difficulty when upscaling astaxanthin production. In this research, a small-scale angled twin-layer porous substrate photobioreactor (TL-PSBR) was used to cultivate green stage biomass of <i>H. pluvialis</i>. Under low light intensities of 20–80 µmol photons m⁻²·s⁻¹, algae in the biofilm consisted exclusively of non-motile vegetative cells (green palmella cells) after ten days of culturing. The optimal initial biomass density was 6.5 g·m⁻², and the dry biomass productivity at a light intensity of 80 µmol photons m⁻²·s⁻¹ was 6.5 g·m⁻²·d⁻¹. The green stage biomass of <i>H. pluvialis</i> created in this small-scale angled TL-PSBR can be easily harvested and directly used as the source of material for the inoculation of a pilot-scale TL-PSBR for the production of astaxanthin.