Estimation of design flood for a given return period is of utmost importance for planning and design of hydraulic structures, river protection works and development of water resources projects. For this purpose, Synthetic Unit Hydrograph (SUH) is generally considered for estimation of design flood as well as development of flood hydrograph for ungauged basins have catchment area of more than 25 km2. For ungauged catchments, the observed rainfall data is used for estimation of rainfall by adopting probability distribution, which becomes an important input for computation of design flood. In this paper, the Extreme Value Type-1 (EV1) distribution is applied in estimating the rainfall, which is evaluated by Anderson–Darling Goodness-of-Fit (GoF) test. This paper presents a study on estimation of design flood at three ungauged catchments of river Sutlej viz., (i) Saisso Khad upto Giabong village (ii) Saisso Khad between Giabong and Rushkling villages and (iii) Kannam Nallah up to Kannam by adopting SUH approach as its catchment areas are more than 25 km2. The annual 1-day maximum rainfall series pertaining to Pooh rain-gauge station is used to estimate the rainfall by adopting EV1 and the results are evaluated through GoF test. The rainfall depth is used for estimation of design flood by applying the procedures as described in Central Water Commission flood estimation report for Western Himalayas-Zone 7. The paper presents that the estimated design flood using SUH approach and the derived flood hydrograph of three ungauged catchments in the tributaries of river Sutlej with 25-year, 50-year, 100-year return period rainfall depth and observed 1-day maximum rainfall could be considered for flood protection and river training works, and development of water resources projects in the region.