The invention provides an in-situ soil pressure testing device and method, and belongs to an underground engineering in-situ stress testing device and method. The in-situ soil pressure testing device comprises steel rings, miniature rubber capsules and transparent soft guide tubes, wherein each steel ring is provided with a guide tube hole, positioning holes and connecting holes; the miniature rubber capsules are fully filled with a colored liquid; and the miniature rubber capsules are in seal connection with the transparent soft guide tubes, and connected with a supporting frame through the positioning holes. According to the quantity of required observation points, a plurality of the steel rings where the miniature rubber capsules and the transparent soft guide tubes are fixed are connected in series by a steel bar connecting rod to form a steel ring string, and the transparent soft guide tubes are led out of the ground through the guide tube holes formed in the steel rings; during an in-situ soil pressure test, the steel ring string where the miniature rubber capsules are fixed is put into a specific drill hole, and the soil pressure of each observation point can be indirectly acquired by observing the heights of liquid columns in the transparent soft guide tubes; the in-situ soil pressure testing device is simple in structure, convenient to operate, low in cost, high in testing precision, and particularly suitable for accurate and quick testing of the soil pressure of a supporting structure-soil interface in foundation pit engineering.