Model tests under 1g condition and numerical simulations of spudcan penetration in the silty fine sand were conducted to study effects of spudcan penetration on the p-delta effect of adjacent free-head and elastic-head piles subjected to lateral and vertical head loads. The p-delta factors were defined and determined based on the maximum pile shaft bending moments and pile head deflections before and after spudcan penetration, which were used to analyze the variations of the p-delta effect with the spudcan penetration depth. The conclusions were obtained as follows. The p-delta effect depends on the pile head constraint condition, the direction of the lateral pile head load and the spudcan penetration depth. For a free-head pile, the p-delta factors decrease with increasing the spudcan penetration depth. For an elastic-head pile, the p-delta factors also decrease during spudcan penetration and the decreases depend on the spudcan penetration depth and the lateral pile head load direction. The decrease associated with the lateral load direction facing back to the spudcan is larger than that associated with the lateral load direction facing to the spudcan. Therefore, the spudcan penetration does not increase the p-delta effect of adjacent piles subjected to lateral and vertical head loads. But the maximum bending moment and its occurring position change during spudcan penetration.