In recent years, small-borehole wireline coring has become increasingly dependent on trajectory control, downhole condition sensing, and real-time directional decision-making. However, under low-flow conditions, conventional MWD pulser heads tend to generate relatively small pulse amplitudes; as hole depth increases, the pressure signal undergoes stronger attenuation and becomes more susceptible to noise interference, making it difficult to sustain a decodable amplitude under a limited pump-pressure budget. Existing studies have mainly focused on surface decoding and signal processing and therefore do not improve, at the source-structure level, the amplitude output and tool-section incremental pressure loss in low-flow operation. Accordingly, this study develops a compact small-diameter mud-pulse pulser head for 1–3 L/s operation and evaluates its performance through an integrated workflow combining theoretical screening, numerical simulation, and shallow-hole field testing focused on hydraulic pulse generation and surface detectability. The results show that, after selecting appropriate bypass-orifice sets, the proposed pulser head produces stable pressure pulses meeting the surface decoding threshold across 1–3 L/s, while maintaining the tool-section incremental pressure loss within 0.5 MPa over the main operating range. The findings further indicate that, in low-flow regimes, the achievable decoding margin and the incremental-loss ceiling are primarily governed by the upstream hydraulic architecture. This work provides a practical basis for reliable low-flow mud-pulse telemetry in small-borehole wireline coring.